Page 392 - Basic College Mathematics with Early Integers

S E C T I O N 5.2 I PROPORTIONS 369

Example 7 Find the unknown number n. PRACTICE 7
n 0.8 Find the unknown number n.
= n 0.7
3 1.5 =
6 1.2
Solution:
Step 1:

n = 0.8
3 1.5

#
#
n 1.5 = 3 0.8 Set the cross products equal to each other.
#
n 1.5 = 2.4 Multiply.
Step 2:
2.4
n = Divide 2.4 by 1.5, the number multiplied by n.
1.5
n = 1.6 Simplify.

Check: Check to see that 1.6 is the unknown number.
Work Practice 7

Example 8 Find the unknown number n. PRACTICE 8

2 Find the unknown number n.
1 1
3 n 4
= n 2
1 3 =
3 2 1 3
4 5 4 1
3 4
Solution:
Step 1:

1s
n
3~ 2E

2 3 1
1 # 2 = 3 # n Set the cross products equal to each other.
3 5 4
1
#
13 1 2 # 3 5 13 5 13 13
#
= 3 # n Multiply. 1 3 2 5 = 3 5 = 3 # = 3
3 4 5
1
13 13 1 13
= # n Write 3 4 as 4 .
3 4
Step 2:
13 13 13 13
, = n Divide by , the number multiplied by n.
3 4 3 4
or
13 4 4 1
n = # = or 1 Divide by multiplying by the reciprocal.
3 13 3 3
1
Check: Check to see that 1 is the unknown number.
3 Answers
1
Work Practice 8 7. n = 3.5 8. n = 11 7