Unit 1 Revision Exercise: Approximation & Estimation
Mathematics
Date:
Name:
Time:
Form: (
)
Multiple Choice Section
1. Correct 243.56 to the nearest unit.
A. 240
B. 243
C. 243.6
D. 244
2. Correct 50.997 to 2 decimal places.
A. 50.00
B. 50.10
C. 50.90
D. 51.00
3. Correct 0.037 48 m 2 to the nearest cm 2 .
A. 3.748 cm 2
B. 3.75 cm 2
C. 37.5 cm 2
D. 375 cm 2
4. Find the length of line segment XV in the following figure, correct to the nearest cm.
X
0 1
cm
V
2
3
4
5
6
7
8
A. 10 cm
P.1
9
10
11
B. 10.2 cm
C. 10.5 cm
D. 11 cm
5. Which of the following units is the most suitable for measuring the time required to travel
from Hong Kong to U.S.A. by plane?
A. second
B. minute
C. hour
D. year
6. What is the precision of the following instru ment?
mL
36
30
24
18
12
6
A. 5 mL
B. 6 mL
C. 10 mL
D. 36 mL
7. Find the measured temperature and the precision of the thermometer shown below.
C
0
10
20
30
40
A. Temperature = 24°C, precision = 0.5°C
B. Temperature = 24°C, precision = 1°C
C. Temperature = 24.5°C, precision = 0.5°C
D. Temperature = 25°C, precision = 1°C
P.2
8. Estimate the size of x.
x
A. 90
B. 200
C. 240
D. 270
9. The capacity of a cup is 72 mL and that of a kettle is approximately equal to 10
3
times of
4
the cup. Estimate the capacity of the kettle.
A. 700 mL
B. 770 mL
C. 840 mL
D. 890 mL
10. The height of Jenny is about 90 cm and her brother is taller than her by 5 heads’ length. If the
length of Jenny’s head is about 19 cm, estimate the height of her brot her.
A. 135 cm
B. 170 cm
C. 175 cm
D. 190 cm
11. The typing speed of Miss Lee is about 38 words per minute. If she needs to type 56 0 words,
estimate the time required.
A. 10 min
B. 14 min
P.3
C. 18 min
D. 22 min
12. Trees are planted long the side of a road at regular intervals of approximately 20 m. Estimate
the number of trees to be planted along a road of 3.978 km long.
A. 160
B. 180
C. 200
D. 220
13. Estimate the area of the shaded region.
0.6 cm
0.6 cm
A. 1.8 cm 2
B. 3.2 cm 2
C. 5 cm 2
D. 9 cm 2
14. The total weight of 40 students is 1 247 kg. If a boat can carry 250 kg only, estimate the
number of boats required to carry all the students.
A. 4
B. 5
C. 8
D. 16
15. The price of a pack of chocolate is $4.9. If Johnson has $70, estimate the number of packs of
chocolate he can buy.
P.4
A. 10
B. 14
C. 15
D. 18
16. The following is the price list of some food and drink. If Ken wants to buy two boxes of
lemon tea, 1 chicken leg and 3 sandwiches, estimate the total pr ice.
Item
Dim-sum
Sandwich
Potato Chips
Chicken Leg
Lemon Tea
$4.7
$15.9
$6.8
$10.7
$7.8
Price
(per unit)
A. $60
B. $65
C. $69
D. $75
17. Using the strategy of reformulation, round off each number in the following expressi on to the
nearest unit.
0.849 + 5.77 − 3.44
A. 0 + 6 − 3
B. 1 + 6 − 3
C. 0.8 + 5 − 3
D. 0.9 + 6 − 3
18. Write down the third significant figure in 5.004 87.
A. 0
B. 4
C. 7
D. 8
19. What is the number of significant figures in 0.004 411?
P.5
A. 2
B. 4
C. 6
D. 7
20. Change
11
into a decimal number, correct to 3 significant figures.
660
A. 0.016
B. 0.017
C. 0.016 6
D. 0.016 7
21. A motor cycle can travel 0.55 km in a minute. Find the speed of the motor cycle in m/s.
(Correct your answer to 3 significant figures.)
A. 0.55 m/s
B. 0.917 m/s
C. 9.17 m/s
D. 550 m/s
22. John spent 11.06 s (correct to 4 significant figures) to complete a 100 m race. Find the
maximum absolute error of John’s record.
A. 0.005 s
B. 0.01 s
C. 0.05 s
D. 0.5 s
23. The weight of a steak should be 442 g (correct to the nearest g) in order to fulfill the quality
control requirement. Which of the following weights is not acceptable?
A. 441.49 g
B. 441.59 g
C. 442.3 g
D. 442.45 g
P.6
24. Peter spends 16.2 minutes (correct to the nearest 0.1 minute) on the Internet everyday. Find
the percentage error. (Correct your answer to 2 decimal places.)
A. 0.31%
B. 0.62%
C. 3.1%
D. 6.2%
25. The weight of a bean is 0.35 g with a percentage error of 6%. Find the maximum absolute
error of this measurement.
A. 0.012 g
B. 0.021 g
C. 0.171 g
D. 5.833 g
26. The length of a side of a square tile is 10.42 cm, correct to the nearest 0.01 cm. Find the range
of the true length of the square tile.
A. Between 10.405 cm and 10.435 cm
B. Between 10.415 cm and 10.425 cm
C. Between 10.42 cm and 10.43 cm
D. Between 10.37 cm and 10.47 cm
P.7
Section A(1)
1. Choose the suitable units from the brackets for the follo wing measurements.
(mm, cm, m, km)
(a) The length of a
(b) The length of a
photo album
(c) The distance between the
basketball field
Kwun Tong station and the
Tsuen Wan station
Tsuen Wan
Kwun Tong
2. Choose the suitable units from the brackets for the following measurements. (mg, g, kg)
(a) The weight of a nail
(b) The weight of an adult
(c) The weight of a battery
3. Write down the precision of each of the following instruments.
(a)
(b)
0
1
2
3
4
0
5 cm
1
2
4. Write down the precision of each of the following instruments.
(a)
(b)
P.8
3
4
5 cm
5. Find the length of the pencil in the following figure, correct to the nearest
(a) cm.
0
cm
1
(b) 0.5 cm.
2
3
4
5
6
7
8
(c) 0.1 cm.
9
10
6. Find the volume of water in the cylinder, correct to the nearest
(a) 10 cm 3 .
30
(b) 5 cm 3 .
(c) cm 3 .
35 cm3
30
25
25
20
7. Measure the length of the line segment AB, correct to the nearest
(a) 0.5 cm.
A
(b) 0.1 cm.
B
8. Correct the following numbers to 2 significant figures.
(a) 94 675
(b) 28.48
(c) 104.59
(d) 0.498 1
9. Correct the following numbers to 3 significant figures.
(a) 237 821
(b) 599.58
(c) 0.001 428
(d) 0.058 39
10. Estimate the values of the following expressions and state the estimation strategies used.
(a) 68 + 52 + 98 + 58 + 12 + 31 + 43
(b) 5.97 + 3.21 + 6.09 + 4.89 + 8.81 + 9.19 + 2.51
P.9
11. Estimate the values of the following expressions and state the estimation strategies used.
(a) 159.59  0.45
(b) 27.66  3.58 + 119.57  6.29
12. The population of City A is 376 894. Find the population, correct to
(a) 1 significant figure.
(b) 2 significant figures.
(c) 4 significant figures.
13. Write down the number of significant figures in each of the following numbers.
(a) 4.57
(b) 2.090
(c) 5 870
(d) 28 900
14. The length, width and height of a train compartment are 42.5 m, 2.5 m and 3.0 m respectively.
If the length, width and height of a cargo container are 13.3 m, 2.3 m and 2.7 m respectively,
estimate the number of cargo containers that a train compartment can c arry.
15. The electricity charge of the Chan’s family is $689.56 this month. If the electricity charge per
unit is $0.38, find the number of units of electricity the Chan’s family consumed this month.
16. To which digits are the following measurements corrected? Then find the maximum absolute
error, upper limit and lower limit of each measurement.
(a) 149 km
(b) 25.6 cm
(c) 0.28 mm
(d) 2.718 2 m
17. In an experiment, the temperature of a glass of solution is 48.5C (corrected to the nearest
0.1C). Find the maximum absolute error, upper limit and lower limit of the temperature.
18. In a 100 m race, the record made by May was 14.24 seconds, correct to the nearest 0.01
second. Find the maximum absolute error and the relative error of this recor d.
P.10
19. The length of the classroom is measured to be 18.8 m, correct to 3 significant figures. Find
the maximum absolute error and the percentage error of the measurement.
(Correct your answer to 3 significant figures. )
22
as the estimation of  and then find the percentage error. Firstly, he changes
7
20. David uses
22
into a decimal number and the answer is corrected to 5 significant figures. Then he uses
7
3.141 6 as the true value of . Find the percentage error in David’s estimation.
(Correct your answer to 4 significant figures. )
Section A(2)
21. The number of pages of a book is about 200. If there is approximately 26 words in a certain
line of a certain page, and there is about 60 lines in that page, es timate the number of words
in the book.
22. In the following figures, the same volume of water is put into cylinders A, B and C
respectively.
C
B
A
cm3
100
80
60
40
20
cm3
100
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
(a) Which cylinder is the most precise?
(b) (i)
cm3
100
Find the volume of water in cylinder A.
(ii) Find the volume of water in cylinder B.
(iii) Find the volume of water in cylinder C.
P.11
23. In Figure A, the area of each square is 1 cm 2 , and in Figure B, each square has an area of 0.25
cm 2 .
Figure A
Figure B
(a) Find the approximate area of the figure in Figure A.
(b) Find the approximate area of the figure in Figure B.
(c) Which one gives a more precise result?
24. Find the approximate area of the figure by using two pieces of square paper A and B. Which
one gives a more precise result?
Square paper A
Square paper B
Area of each square = 1 cm 2
Area of each square = 0.25 cm 2
25. Estimate the values of the following expressions and state the estimation strategies used.
(a) 48.92 +50.01 + 121.99 + 98.84 + 42.13 + 89.48 + 31.82
(b) 3.09 × 4.21 + 1 871  51
P.12
26. The height of Denny is 4 feet 8 inches. If 1 feet = 12 inches and 1 inch = 2.54 cm, find the
height of Denny in cm. (Correct your answer to 3 significant figures.)
27. The weight of a box of candies is 785 g. If the relative error of the measurement is
1
,
2 000
find the maximum absolute error of this measurement. (Correct your answer to 3 significant
figures.)
28. The length of the equator of the earth is measured to be 12 756 km. If the percentage error is
0.1%, find the maximum absolute error of this measurement.
(Correct your answer to 2 significant figures.)
29. The distance between the earth and the moon is measured to be 385 000 km. If the percentage
error is 2%, find the range of the true distance.
30. Mary measured the weight of 50 $1 coins and the measurement is 350 g, correct to the nearest
g.
(a) Find the percentage error of this measurement.
(b) If Mary uses the weight of 50 $1 coins to estimate the weight of each $1 coin, find the
maximum absolute error of the weight of each $1 coin.
(c) If the true weight of each $1 coin is 7.02 g, using the result of (b), find the percentage
error of the weight of each $1 coin.
(Correct your answer to 2 significant figures if necessary. )
31. Sammy measures the length of a rope and the measurement is corrected to the nearest 0.1 cm.
(a) Find the maximum absolute error of the measurement.
(b) If the percentage error of the measurement is 1.4%, find the measured length of the rope.
(Correct your answer to 2 significant figures.)
(c) Find the range of the true length of the rope.
P.13
Section B
32. The approximate values of x and y are 7.5 and 3.5 respectively, correct to 2 significant
figures.
(a) Find the upper limits and lower limits of x and y respectively.
(b) Find the upper limit and lower limit of x + y.
(c) Find the upper limit and lower limit of x − y.
33. The base and the height of a parallelogram are 12.3 cm and 5.6 cm respectively, correct to 2
significant figures.
(a) Find the upper limits and lower limits of the base and the height of the parallelogram
respectively.
(b) Find the upper limit and lower limit of the area of the parallelogram.
(Correct your answer to 3 significant figures. )
P.14
Answer
Multiple Choice Section
1. D
243.56 = 244 (corr. to the nearest unit)
2. D
50.997 = 51.00 (corr. to 2 d.p.)
3. D
∵
1 m = 100 cm
1 m 2 = (100  100) cm 2
= 10 000 cm 2
∴
0.037 48 m2 = 374.8 cm 2
= 375 cm 2 (corr. to the nearest cm 2 )
4. A
∵
The distance between X and V is about 10 cm to 11 cm, and the point V is closer to the
mark of 10 cm than 11cm.
∴
The length of line segment XV is approximately 10 cm.
5. C
The most suitable unit is hour.
6. B
∵ The precision of the instrument = The differen ce between consecutive markings
∴ Precision = 6 mL
P.15
7. B
∵ The measured temperature is about 24C to 25C, and it is closer to the mark of 24C
than 25C; the precision of the thermometer is the difference between consecutive
markings.
∴ Temperature = 24C, precision = 1C
8. D
∵ The size of x is approximately equal to that of 3 right angles.
∴ The size of x is approximately 270°.
9. B
∵
72 mL  70 mL and 10
3
 11
4
∴ The capacity of the kettle is approximately (70  11) mL = 770 mL
10. D
∵
19 cm  20 cm
∴
The height of Jenny’s brother is about (90 + 20  5) cm = 190 cm
11. B
∵ 38 words  40 words
∴ The time required is approximately (560  40) min = 14 min
12. C
Length of the road = 3.978 km
= 3 978 m
 3 980 m
Number of trees to be planted is approximately
∴ About 200 trees are to be planted.
P.16
3 980
+ 1 = 200
20
13. A
0.6 cm
0.6 cm
1
3
2
4
5
Area of each square = (0.6  0.6) cm = 0.36 cm
2
∴
2
Area of the shaded region is approximately (0.36  5) cm = 1.8 cm
2
14. B
Total weight of 40 students = 1 247 kg
 1 250 kg
∴
Number of boats required is approximately
15. B
70  4.9  70  5
= 14
∴
Johnson can buy 14 packs of chocolate.
16. D
Total price = $7.8  2 + $10.7 + $15.9  3
 $8  2 + $11 + $16  3
P.17
1 250
=5
250
2
= $16 + $11 + $48
= $75
17. B
∵
0.849 = 1 (corr. to the nearest unit)
5.77 = 6 (corr. to the nearest unit)
3.44 = 3 (corr. to the nearest unit)
∴
0.849 + 5.77 − 3.44  1 + 6 − 3
18. A
∵
The zeroes between 5 and 4 are significant figures.
∴
The third significant figure in 5.004 87 is 0.
19. B
For a number between 0 and 1, the most important digit starts from the first non -zero figure
from the left.
∴
There are 4 significant figures in 0.004 411.
20. D
11
= 0.016 7 (corr. to 3 sig. fig.)
660
21. C
Speed =
=
Distance
Time
0.55  1 000
m/s
60
= 9.17 m/s (corr. to 3 sig. fig.)
P.18
22. A
Maximum absolute error =
0.01 s
2
= 0.005 s
23. A
Upper limit of the weight = (442 + 0.5) g
= 442 .5 g
Lower limit of the weight = (442 − 0.5) g
= 441 .5 g
∴
A steak which weighs 441.49 g is not acceptable.
24. A
Percentage error =
0.1
2
16.2
 100 %
= 0.31% (corr. to 2 d.p.)
25. B
Maximum absolute error = (0.35  6%) g
= 0.021 g
26. B
0.01 cm
2
= 0.005 cm
Maximum absolute error =
∴
The range of true length of the square tile is between 10.415 cm and 10.425 cm.
P.19
Section A(1)
1. (a) cm
(b) m
(c) km
2. (a) mg
(b) kg
(c) g
3. (a) 0.1 cm
(b) 1 cm
4. (a) 0.1 g
(b) 0.01 g
5. (a) 8 cm
(b) 7.5 cm
(c) 7.6 cm
6. (a) 30 cm 3
(b) 25 cm 3
(c) 26 cm 3
7. (a) 6.5 cm
(b) 6.7 cm
8. (a) 95 000
(b) 28
P.20
(c) 100
(d) 0.50
9. (a) 238 000
(b) 600
(c) 0.001 43
(d) 0.058 4
10. (a) Using the strategy of reformulation to round off each number to the nearest ten.
∴
68 + 52 + 98 + 58 + 12 + 31 + 43  70 + 50 + 100 + 60 + 10 + 30 + 40
= 360
(b) Using the strategy of reformulation to round off each number to the nearest unit.
∴
5.97 + 3.21 + 6.09 + 4.89 + 8.81 + 9.19 + 2.51  6 + 3 + 6 + 5 + 9 + 9 + 3
= 41
11. (a) Using the strategy of reformulation by changing the numbers to compatible numbers.
∵
159 .59  160 and 0.45 
∴
159 .59  0.45  160 
1
2
1
2
= 80
(b) Using the strategy of reformulation by changing the numbers to compatible numbers.
∵
27 .66  28 , 3.58  4 , 119 .57  120 , 6.29  6
∴
27.66  3.58 + 119 .57  6.29  28  4 + 120  6
= 7 + 20
= 27
12. (a) Population = 400 000 (corr. to 1 sig. fig.)
P.21
(b) Population = 380 000 (corr. to 2 sig. fig.)
(c) Population = 376 900 (corr. to 4 sig. fig.)
13. (a) 3
(b) 4
(c) 3 or 4
(d) 3, 4 or 5
14. ∵
∴
Length of the train compartment  42 m, length of the cargo container  13.5 m
Based on the respective lengths, the number of cargo containers that can be carried

42
3
13.5
∵
Width of the train compartment = 2.5 m, width of the cargo container = 2.3 m
∴
Based on the respective widths, the number of cargo containers that can be carried
=
2.5
1
2.3
∵
Height of the train compartment = 3.0 m, height of the cargo container = 2.7 m
∴
Based on the respective heights, the number of cargo containers that can be carried
=
∴
15. ∵
∴
3.0
1
2.7
Number of cargo containers that the train compartment can carry  3  1  1 = 3
Electricity charge  $690, electricity charge per unit  $0.4
690
0.4
= 1 725
Number of units of electricity consumed 
P.22
16. (a) 149 km is corrected to the nearest 1 km .
The maximum absolute error =
1 km
2
= 0.5 km
Upper limit = (149 + 0.5) km
= 149.5 km
Lower limit = (149 − 0.5) km
= 148.5 km
(b) 25.6 cm is corrected to the nearest 0.1 cm .
The maximum absolute error =
0.1 cm
2
= 0.05 cm
Upper limit = (25.6 + 0.05) cm
= 25.65 cm
Lower limit = (25.6 − 0.05) cm
= 25.55 cm
(c) 0.28 mm is corrected to the nearest 0.01 mm .
The maximum absolute error =
0.01 mm
2
= 0.005 mm
Upper limit = (0.28 + 0.005) mm
P.23
= 0.285 mm
Lower limit = (0.28 − 0.005) mm
= 0.275 mm
(d) 2.718 2 m is corrected to the nearest 0.000 1 m .
The maximum absolute error =
0.000 1 m
2
= 0.000 05 m
Upper limit = (2.718 2 + 0.000 05) m
= 2.718 25 m
Lower limit = (2.718 2 − 0.000 05) m
= 2.718 15 m
17. ∵
∴
The temperature is corrected to the nearest 0.1 C .
The maximum absolute error =
0.1 C
2
= 0.05 C
Upper limit = (48.5 + 0.05) C
= 48.55 C
Lower limit = (48.5 − 0.05) C
= 48.45 C
P.24
0.01 second
2
= 0.005 second
18. The maximum absolute error =
0.005
14 .24
1
=
2 848
The relative error =
0 .1 m
2
= 0.05 m
19. The maximum absolute error =
The percentage error =
0.05
 100 %
18.8
= 0.266% (corr. to 3 sig. fig.)
20.
22
= 3.142 9 (corr. to 5 sig. fig.)
7
The percentage error =
3.142 9 − 3.141 6
 100%
3.141 6
= 0.041 38% (corr. to 4 sig. fig.)
Section A(2)
21. The number of words is approximately 200  26  60 = 312 000
22. (a)
(i) 60 cm 3
(ii) 60 cm 3
(iii) 64 cm 3
(b)
Cylinder C
23. (a) The figure occupies about 10 squares.
P.25
∴
Area of the figure is approximately (1  10) cm 2 = 10 cm 2
(b) The figure occupies about 42 squares.
∴
Area of the figure is approximately (0.25  42) cm2 = 10.5 cm 2
(c) Figure B
24. Area of the figure in square paper A is approximately (1  19) cm 2 = 19 cm 2
Area of the figure in square paper B is approximately (0.25  74) cm 2 = 18.5 cm 2
∴
Squa re pa per B gives a more precise result.
25. (a) Using the strategy of reformulation to round off each number to the nearest ten.
∴
48.92 + 50.01 + 121 .99 + 98.84 + 42.13 + 89.48 + 31.82
 50 + 50 + 120 + 100 + 40 + 90 + 30
= 480
(b) Using the strategy of reformulation by changing the numbers to compatible numbers.
∵
3.09  3 , 4.21  4 , 1 871  1 900 , 51  50
∴
3.09  4.21 + 1 871  51
 3  4 + 1 900  50
= 12 + 38
= 50
26. 4 feet 8 inches = (4  12 + 8) inches = 56 inches
∵
1 inch = 2.54 cm
∴
The height of Denny = (56  2.54) cm
= 142 cm (corr. to 3 sig. fig.)
27. Let the maximum absolute error be x g.
x
1
=
785
2 000
P.26
x=
785
2 000
= 0.393 (corr. to 3 sig. fig.)
∴
The ma ximum a bsolu te error of this measuremen t is 0.393 g.
28. Let the maximum absolute error be x km.
x
0.1
=
12 756
100
x=
12 756  0.1
100
= 13 (corr. to 2 sig. fig.)
∴
The ma ximu m a bsolu te er ror of this measu remen t is 13 k m.
29. Let the maximum absolute error be x km.
x
2
=
385 000 100
385 000  2
x=
100
= 7 700
∴
The maximum absolute error = 7 700 km
Upper limit = (385 000 + 7 700) km
= 392 700 km
Lower limit = (385 000 − 7 700) km
= 377 300 km
∴
The ra nge of the true dista nce is bet ween 377 300 km a nd 392 700 km.
30. (a) The maximum absolute error =
1g
2
= 0.5 g
P.27
The percentage error =
0.5
 100 %
350
= 0.14% (corr. to 2 sig. fig.)
(b)
∵ The maximum absolute error of the weight of 5 0 $1 coins = 0.5 g
∴ The maximum absolute error of the weight of each $1 coin =
0.5 g
50
= 0.01 g
(c)
Using the result of (b), the maximum absolute error = 0.01 g
∴ The percentage error =
0.01
 100 %
7.02
= 0.14% (corr. to 2 sig. fig.)
31. (a) The maximum absolute error =
0.1 cm
2
= 0.05 cm
(b) Let the measurement of the length of the rope be x cm.
∵ The percentage error = 1.4%
∴
0.05 1.4
=
100
x
x=
100  0.05
1.4
= 3.6 (corr. to 2 sig. fig.)
∴
The measured lengt h of the rope is 3.6 cm.
(c) Upper limit = (3.6 + 0.05) cm
= 3.65 cm
Lower limit = (3.6 − 0.05) cm
= 3.55 cm
∴
The ra nge of the true lengt h of the rope is bet ween 3.55 cm a nd 3.65 cm.
Section B
P.28
32. (a) Upper limit of x = 7.5 + (
0.1
)
2
= 7.55
Lower limit of x = 7.5 − (
0.1
)
2
= 7.45
Upper limit of y = 3.5 + (
0.1
)
2
= 3.55
Lower limit of y = 3.5 − (
0.1
)
2
= 3.45
(b) Upper limit of (x + y) =Upper limit of x + Upper limit of y
= 7.55 + 3.55
= 11.1
Lower limit of (x + y) = Lower limit of x + Lower limit of y
= 7.45 + 3.45
= 10.9
(c) Upper limit of (x − y) = Upper limit of x − Lower limit of y
= 7.55 − 3.45
= 4.1
Lower limit of (x − y) = Lower limit of x − Upper limit of y
= 7.45 − 3.55
= 3.9
33. (a) Upper limit of the base = (12.3 +
0.1
) cm = 12.35 cm
2
Lower limit of the base = (12.3 −
0.1
) cm = 12.25 cm
2
P.29
Upper limit of the height = (5.6 +
0.1
) cm = 5.65 cm
2
Lower limit of the height = (5.6 −
0.1
) cm = 5.55 cm
2
(b) Upper limit of the area = Upper limit of the base  Upper limit of the height
= (12.35  5.65) cm 2
= 69.8 cm 2 (corr. to 3 sig. fig.)
Lower limit of the area = Lower limit of the base  Lower limit of the height
= (12.25  5.55) cm 2
= 68.0 cm 2 (corr. to 3 sig. fig.)
P.30