COURSE 2 LESSON 2-2
Using Number Sense to Solve Equations
Find the solution of h – 18 = 54: 3, 36, 62, or 72.
You can test each number by substituting h in the equation.
3 – 18
– 15 = 54
62 – 18
36 – 18
54
False
54
18 = 54
72 – 18
54
44 = 54 False
False
54
54 = 54
True
Since the equation is true when you substitute 72 for h, the solution is 72.
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COURSE 2 LESSON 2-2
Using Number Sense to Solve Equations
Use mental math to solve each equation.
a. s – 9 = 5
b. 4z = 28
What you think
What you think
What number minus 9 equals 5?
What number times 4 equals 28?
Since 14 – 9 = 5, s = 14.
Since 4 • 7 = 28, z = 7.
c. g + 7 = 11
d. c = 5
6
What you think
What you think
What number plus 7 equals 11?
What number divided by 6 equals 5?
Since 4 + 7 = 11, g = 4.
Since 30 ÷ 6 = 5, c = 30.
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COURSE 2 LESSON 2-2
Using Number Sense to Solve Equations
The weight of a packing crate is 14.65 lb. The crate
and its contents together weigh 85.21 lb. Estimate the weight of
the contents.
Words
crate’s
weight
Let
Equation
c
plus
contents’
weight
equals
total
weight
= the weight of the contents.
14.65
14.65 + c = 85.21
14.65
15
85.21
15 + c = 85
c = 70
+
c
85
=
85.21
Choose compatible numbers.
What number added to 15 is 85?
Use mental math.
The contents of the crate weigh about 70 lb.
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COURSE 2 LESSON 2-2
Using Number Sense to Solve Equations
Solve each equation. Use mental math or estimation.
1. q – 15 = 25
q = 40
4. 80 = 8
t
t = 10
2. 6r = 42
3. 17.25 + s = 21.4
r=7
s
5. m – 39.8 = –101.03
m
–61
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