Technical Mathematics, Sixth Edition

1.9. Percentage

Our final topic in this long chapter is the very useful subject of percentage.

1.9.1. Definition of Percent

The word percent means by the hundred, or per hundred. A percent thus gives the number of parts in every hundred.

Example 115: If we say that a certain concrete mix is 12% cement by weight, we mean that 12 lb out of every 100 lb of mix will be cement.

The word rate is often used to indicate a percent, or percentage rate, as in "rejection rate," "rate of inflation," or "growth rate."

Example 116: A failure rate of 2% means that, on average, 2 parts out of every 100 would be expected to fail.

Percent is another way of expressing a fraction having 100 as the denominator.

Example 117: If we say that a builder has finished 75% of a house, we mean that he has finished of the house.

1.9.2. Converting to Percent

Before working some percentage problems, let us first get some practice in converting decimals and fractions to percents, and vice versa. To convert decimals to percent, simply move the decimal point two places to the right and affix the percent symbol (%).

Example 118: Here we convert decimals to percent. 0.75 = 75% 3.65 = 365% 0.003 = 0.3% 1.05 = 105%

To convert fractions or mixed numbers to percent, first write the fraction or mixed number as a decimal, and then proceed as above.

Example 119: = 0.25 = 25% = 2.5 = 250% = 1.25 = 125%

1.9.3. Converting ...