Basic Math Operations - Mathematics and Statistics for the Environment - page 43

• When using percentage in calculations (such as when used to calculate hypochlorite dos-
ages and when the percent available chlorine must be considered), the percentage must be
converted to an equivalent decimal number; this is accomplished by dividing the percent-
age by 100. For example, calcium 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 irst 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
50

ft
ft

= 052 . (decimalequivalent)

052 . ×= 100 5 2

Thus, the tank is 52% full.

■ EXAMPLE 2.1
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:

325 gal
6500 gal

Percent = × 100 = 5%

■ EXAMPLE 2.2
Problem: Convert 65% to decimal percent.

Solution:

Percent 65

100

DecimalPercent = = = 065 .

100

■ EXAMPLE 2.3
Problem: Biosolids contains 5.8% solids. What is the concentration of solids in decimal percent?

Solution:

58
100

.%

Decimalpercent = = 0 058 .

Note: Unless otherwise noted, all calculations in the text using percent values require the percent
to be converted to a decimal before use.

Key Point: To determine what quantity a percent equals, first convert the percent to a decimal then
multiply by the total quantity:

Quantity = Total × Decimal percent (2.2)