Ratios and Proportions - Basic Mathematics for Water and Wastewater Operators - page 131

Solution : First, analyze the problem. Here, the unknown is some number of hours.
But should the answer be larger or smaller than 20 hours? If a 4-gpm pump can fill
the tank in 20 hours, a larger pump (10-gpm) should be able to complete the filling
in less than 20 hours. Therefore, the answer should be less than 20 hours. Now set
up the proportion:

hr
20 hr

x 4 gpm

10 gpm

=

20 × 4

x =

10

= 8hr

■ Example 9.2

Problem : Solve for x in the proportion problem given below.

36
180

= x

4450

Solution:

4450 × 36

= x

180
890 = x

■ Example 9.3
Problem : Solve for the unknown value x in the problem given below.

34
2

. = 6

x

Solution:

34 . ×=× x 26

26
34

× == 12

3.4

x = 3.53

.

■ Example 9.4
Problem : One pound of chlorine is dissolved in 65 gallons of water. To maintain the
same concentration, how many pounds of chlorine would have to be dissolved in 150
gallons of water?