# Percents

*percent*means “divided by one hundred.” When you see the word “percent,” or the symbol %, remember it means.

For example,

25 percent

To convert a decimal into a percent, move the decimal point two places to the right.

For example,

Conversely, to convert a percent into a decimal, move the decimal point two places to the left.

For example,

For example,

For example,

**Note: **Percent problems often require you to translate a sentence into a mathematical equation.

*What percent of 25 is 5?*

*A. 10%
B. 20%
C. 30%
D. 35%
E. 40%*

Translate the sentence into a mathematical equation as follows:

What | percent | of | 25 | is | 5 |

x |
. |
25 | = | 5 |

*x* = 20

The answer is (B).

*2 is 10% of what number*

*A. 10
B. 12
C. 20
D. 24
E. 32*

Translate the sentence into a mathematical equation as follows:

2 | is | 10 | % | of | what number |

2 | = | 10 | . | x |

20 = *x*

The answer is (C).

*What percent of a is 3a ?*

*A. 100%
B. 150%
C. 200%
D. 300%
E. 350%*

Translate the sentence into a mathematical equation as follows:

What | percent | of | a |
is | 3a |

x |
. |
a |
= | 3a |

(by canceling the *a*’s)

*x* = 300

The answer is (D).

*If there are 15 boys and 25 girls in a class, what percent of the class is boys?*

*A. 10%
B. 15%
C. 18%
D. 25%
E. 37.5%*

The total number of students in the class is 15 + 25 = 40. Now, translate the main part of the sentence into a mathematical equation:

what | percent | of | the class |
is | boys |

x |
. |
40 | = | 15 |

2*x* = 75

*x* = 37.5

The answer is (E).

**Note:**Often you will need to find the percent of increase (or decrease). To find it, calculate the increase (or decrease) and divide it by the original amount:

**Percent of change:**

*The population of a town was 12,000, and ten years later it was 16,000. What was the percent increase in the population of the town during this period?*

*A.
B. 50%
C. 75%
D. 80%
E. 120%*

The population increased from 12,000 to 16,000.

Hence, the change in population was 4,000.

Now, translate the main part of the sentence into a mathematical equation:

Percent of change:

The answer is (A).