Question

There are 160 people in a grade. The ratio of boys to girls is 3 to 5. Which proportion can you use to find the number x of boys?

Answer 1

3/8 = x/160

Explanation:

First, you need to find the total amount of boys and girls, so you add 3+5.

3+5= 8

So 8 is the total, and out of 8 people, 3 of them are boys. Now that you have that, you can set up the first part of the proportion.

3/8

Now, what information does it give you about the people in the grade? It tells you the total amount, but not the number of boys.

3/8 = out of 8 people, 3 of them are boys.

x/160 = out of 160 people in a grade, x of them are boys.

So your final proportion would be 3/8 = x/160.

Bonus:

If you need to find the number of boys in a grade, just solve the proportion as normal, which would give you 60. So there are 60 boys out of 160 people in a grade.

Answer 2

60 boys

Explanation:

boys : girls = 3 : 5

Total number of people = 160

Let y = common factor:

Therefore, 3y + 5y = 160

⇒ 8y = 160

⇒ y = 160 ÷ 8 = 20

Boys = 3y = 3 x 20 = 60

Girls = 5y = 5 x 20 = 100

So there are 60 boys and 100 girls