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

Answer 1

number of boys --- b
number of girls ---- 160-b

b : 160-b = 3 : 5

or

b/(160-b) = 3/5 <------- that's what you asked for

Answer 2

b = boys

g = girls

There are 160 people in a grade means:

b + g = 160

Subtract b to both sides

g = 160 - b

The ratio of boys to girls is 3 to 5 means:

b / g = 3 / 5

Replace g with 160 - b in this equation.

b / ( 160 - b ) = 3 / 5

This is a proportion.

The solution is:

Cross multiply a proportion.

5 b = 3 ( 160 - b )

5 b = 480 - 3 b

Add 3 b to both sides

8 b = 480

b = 480 / 8

b = 60

g = 160 - b =160 - 60

g = 100

Check result:

b + g = 60 + 100 = 160

b / g = 60 / 100 = 20 • 3 / 20 • 5 = 3 / 5

Answer 3

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?