Fractions, Decimals, and Percent - Basic Mathematics for Water and Wastewater Operators - page 101

Part
Whole

Percent (%) = (4.1)

For example, 22 percent (or 22%) means 22 out of 100, or 22/100. Dividing
22 by 100 results in the decimal 0.22:

22
100

22 % == 022 .

• When using percentages in calculations (such as when calculating hypo-

chlorite dosages and when the percent available chlorine must be consid-
ered), the percentage must be converted to an equivalent decimal number;
this is accomplished by dividing the percentage by 100. For example, cal-
cium hypochlorite (HTH) contains 65% available chlorine. What is the
decimal equivalent of 65%? Because 65% means 65 per hundred, divide 65
by 100: 65/100, which is 0.65.

• Decimals and fractions can be converted to percentages. The fraction is

first converted to a decimal, then the decimal is multiplied by 100 to get the
percentage. For example, if a 50-foot-high water tank has 26 feet of water in
it, how full is the tank in terms of the percentage of its capacity?

26 ft
50 ft

= 0.52 (decimalequivalent)

0.52 × 10 00 2 =

Thus, the tank is 52% full.

■ Example 4.4
Problem: The plant operator removes 6500 gal of biosolids from the settling tank.
The biosolids contain 325 gal of solids. What is the percent solids in the biosolids?

Solution:

gal
6500 gal

325

×=% 100 5

■ Example 4.5
Problem : Convert 65% to decimal percent.

Solution:

Percent
100

65
100

Decimalpercent = = = 065 .