4.4 Estimating with
Decimals
Homework
Mental Math
Give a whole-number estimate for these decimal
addition problems. Show which whole numbers
you used:
3.8 + 9.9 = EXAMPLE: 4 + 10 = 14
2.7 + 8.1 =
10.5 – 6.6 =
8.8 + 8.9 =
23.7 – 8.8 =
25.5 + 11.9 =
26.2 – 10.8 =
Math Message
Turn to a tablemate and describe two examples
in which decimals are used in real-life
situations.
Measurement:
Money:
Other:
Why are decimals useful?
SRB Page 26:
Trip Meters and Speedometers
What information would we get if it just showed whole
numbers of miles traveled?
Decimals make it possible to have a more precise
measurement of distance traveled. Below the
speedometer shows tenths of a mile.
Have you traveled closer to 45 miles or 46?
How do I round decimals?
• Rounding decimals are very similar to
rounding whole numbers-the only
difference is there is a decimal point!
• Look at the digit to the right of the place
you are rounding
• Think about this poem
If it is 4 or less just ignore,
If it is 5 or more add one more!
Rounding to the nearest tenth
• Round to the nearest tenth
5.263
– The number to the right of the 2 is a six.
– Six is greater than five, so I need to add one more
the 2. The 2 becomes a 3 and everything after
becomes a 0
– 5.263 rounded to the nearest tenth become 5.300
or 5.3
Rounding to the Nearest
Hundredth
• Round to the nearest hundredth
• Remember 4 or less just ignore, 5 or more
add one more!
• 3.653 The number to the right of the 5 is
an 3. 3 is less than 4, so we just ignoremeaning the five in the hundredths place
stays the same.
• The 5 stays the same and all the other
numbers after it become zeros
The correct answer is: 3.650 or 3.65
More Practice
•
•
•
•
•
•
2.34
46.675
232.23
96.782
0.45
12.322
Estimating Decimal Sums MJ p 85
Must answer the questions by using ESTIMATION,
not by calculating exact answers.
Partnership Work – MJ p. 83
MJ 85
Wrapping it UP!
• In your math notebook, solve the following
problems using estimation.
3.67 + 0.7
5.23 - 1.1
Write one new fact you learned about
estimating decimals.
Homework – Study Link 4.4
Math Box 4.4