6th Grade Math Textbook, Fundamentals

Think

16 • 2 32, so what

number times 2 equals 18?

Lesson 6-3 for exercise sets. &KDSWHU 

&KHFN<RXU3URJUHVVI

Does the pair of ratios form a proportion? Use cross products, simplification,

or proportional reasoning.

1. 
   
   
   
   2. 3.4 : 9 :
   
   
   
   

4.1.2 : 1.8 2.4 : 3.6 5.3.6 : 4.2 4.5 : 5.6 6.1.5 : 2.4 2.7 : 3.6

Find the missing term in each proportion. Then check your work to justify your answer.

7.  8.  9. 

10.Discuss and Write Explain why you could set up a proportion for the

opening problem as  , but you could not set it up as .

?



?



?



225

175

175

225

9

7

9

7

1. 2
   y

0.9

3.6

36

8

n

48

9

t

5

6

4

5

2

5

?

(^6112) 
?
(^1018366) 
?
126 
Use the Cross-Products Rule:
56 : 8 35 : 5
Cross multiply.
56 • 5 8 • 35
280  280 Tr u e
?
?
35
5
(^56) ?
8
1

Here are two ways to find the missing term in a proportion.

The missing term in a proportion can be located

in any of the four positions.

Method 1 Use the Cross-Products Rule

Solve: 

 Cross multiply.

32 n16 • 18



n 9

Check: Substitute 9 for n.

Simplify.

 Tr u e

18

32

9

16

9

16

9

16

Divide both sides by

32 to isolate n.

288

32

32 n

32

(^9) ?
16
18
32
(^9) ?
16
18
32
n
16
18
32
n
16
Method 2 Use Proportional Reasoning
and Mental Math
Solve: 
n 9 9 • 2  18
Check: Substitute 9 for n.
Cross multiply.
9 • 32 16 • 18
288  288 Tr u e
18
32
(^9) ?
16
?
18
32
(^9) ?
16
18
32
n
16
Compare Simplified Ratios:

 not a proportion
1
2
1
3
1
3
12
36
1
3
1
2
14
28
1
2
12
36
(^14) ?
28
2
Use the Cross-Products Rule or simplification to determine
if the ratios form a proportion.