## Proportion

A proportion is how much of something relative to the whole, usually expressed as a percent. To calculate a proportion, divide how much of the thing in question by the whole to get a decimal, and multiply the decimal by 100 to get a percent.
For example, a class of 8 students has 4 boys. To calculate the proportion of boys in the class, do the following:
```boys     = 4
students = 8
decimal  = 4 ÷ 8     = 0.5
percent  = 0.5 × 100 = 50
```
When calculating proportions, you don't necessarily need to divide the exact numbers. If the example above was modified so that a university of 800 students has 400 boys, you could still divide 4 by 8 to get the same proportion.
Sometimes the whole amount is not explicitly given, so to calculate a proportion, first add all of the parts of the whole to get the whole amount. For example, a class has 4 boys and 12 girls. To calculate the proportion of boys in the class, do the following:
```boys              =  4
girls             = 12
students = 4 + 12 = 16
decimal  = 4 ÷ 16     = 0.25
percent  = 0.25 × 100 = 25
```

### Exercise 1 of 6

A jar has 18 chocolate chip cookies and 12 oatmeal raisin cookies. What percent of the cookies are chocolate chip?

### Exercise 2 of 6

A zoo has 108 mammals and 42 reptiles What percent of the animals are mammals?

### Exercise 3 of 6

On a road trip, 3.5 days are in California, 2 days are in Oregon, and 2.5 days are in Washington. What percent of the trip is in California?

### Exercise 4 of 6

A class has 4 boys and 12 girls. A few weeks into the semester, 2 boys and 2 girls join the class. How many percent did the proportion of boys increase?

### Exercise 5 of 6

There are 8 billion people in the world, and 340 million people in the USA. What percent of people live in the USA? To simplify the calculation, treat 8 billion as 8,000 million.

### Exercise 6 of 6

There are 1.48 billion cars in the world, and 37 million of those are electric. What percent of cars are electric? To simplify the calculation, treat 1.48 billion as 1,480 million.