Page 21 - Appplied Mathematics for the Petroleum and Other Industries, 5th Edition

60 NUMBER RELATIONS

yields 0.32. In other words, 32% = 0.32. To change a decimal fraction to percent,
move the decimal point two places to the right and add the percent symbol; for
example, 0.64 becomes 64%.

Example Problem: Find 14% of 430.
Solution:
14% = 0.14
0.14 × 430 = 60.2.
Thus, 14% of 430 is 60.2.
If you have a calculator with a % key, all you do is enter:

430 × 14% = 60.2.

Example Problem: Find 4½% of 85.
Solution:
0.045 × 85 = 3.825,
or, using the calculator,

85 × 4.5% = 3.825.

Base, Rate, and Percentage
RATE × BASE = PERCENTAGE
Base, rate, and percentage are terms used in percentage problems. Base is the
quantity of which a percentage is desired. Rate is a desired percentage of the
base. Percentage is the product of the rate times the base. For example, figure 3.1
shows that 6% of 300 is 18. In this case, 6% is the rate, 300 is the base, and 18 is
6% of 300 is 18
the percentage. The relationship of base, rate, and percentage can be expressed as
Figure 3.1 Percent relations percentage = rate × base.

Three types of percentage problems involve finding one of these elements
when the other two are known. First, when the base and rate are known, percent-
age is found by multiplying the base times the rate.

Example Problem: How much is 8% of $625?
Solution: In this example, 8% is the rate and $625 is the base. So, rate times
base is
$625 × 0.08 = $50.00.
Eight percent of $625 is $50.00.

Petroleum Extension-The University of Texas at Austin
Example Problem: If a woman earns $120 and saves 12½% of it, what per-
centage of her earnings did she save?
Solution:
12½% = 12.5% = 0.125
$120 × 0.125 = $15.00.
The percentage saved is $15.00.