SEE EXAMPLE 1
on p. 423
for Ex. 18
18. ERROR ANALYSIS Describe and correct the
x
4
5ᎏ
.
error in solving the proportion ᎏ
9
18
SEE EXAMPLE 2
19.
on p. 424
for Exs. 19—20
★ MULTIPLE CHOICE
Hair grows an average of 0.5 inch in 1 month.
Choose the proportion that you can use to determine the number of
months m it will take for hair to grow 6 inches.
0.5
6
A ᎏ
5ᎏ
0.5
m
B ᎏ
5ᎏ
m
1
1
0.5
6
C ᎏ
5ᎏ
m
6
m
1
D ᎏ
5ᎏ
1
0.5
6
20. MEASUREMENT There are about 16 kilometers in 10 miles. Write a
proportion you can use to find the number k of kilometers in 250 miles.
21. ESTIMATION There are about 18.3 meters in 20 yards. Estimatee the
number of meters in one yard.
SEE EXAMPLE 3
USING PROPORTIONS Use the ratio of boys to girls and the class size to
on p. 424
for Exs. 22—29
find the number of boys and number of girls in each class.
22. 3 : 5,, 80
23. 5 : 4,, 45
24. 4 : 3,, 35
25. 3 : 4,, 84
26. 7 : 3, 70
27. 5 : 7, 60
28. 2 : 3, 65
29. 6 : 7, 52
SEE EXAMPLE 4
ESTIMATION Estimate to solve the proportion.
on p. 425
for Exs. 30—33
30. } 5 }
0.77
2.4
m
6
4.1
m
4.3
34.5
59.7
35.8
31. } 5 }
83.9
m
32. } 5 }
m
12
44.6
18.7
33. } 5 }
xy ALGEBRA Solve the proportion.
15
4
b23
16
9
2n
34. } 5 }
5
8
3
4
35. } 5 }
a
b
c
d
d
b
x
x13
36. } 5 }
5
2
37. }
5}
t
t26
c
a
38. CHALLENGE If } 5 } , then is } 5 } also true? Explain your reasoning.
In Exercises 39–42, tell whether the ratios form a proportion.
EXTENSION
Deciding Whether Ratios Form a Proportion
Only ratios that form a proportion are equal.
5
ⱨᎏ
ᎏ
9 16
2
2 p 16 ⱨ 9 p 5
32 Þ 45
Write the possible proportion.
Find cross products.
Multiply. The cross products are not equal.
c Answer The ratios don’t form a proportion.
24 3
39. ᎏ
,ᎏ
104 13
426
6 21
40. ᎏ
,ᎏ
7 18
★ 5 STANDARDIZED TEST PRACTICE
3.4 5.6
41. ᎏ
,ᎏ
4.3 6.5
9 54
42. ᎏ
,ᎏ
4.3 25.8
5 HINTS AND HOMEWORK HELP at classzone.com
e