Question

The sides of a triangle are in the ratio 3 : 4 : 5. What is the length of each side if the perimeter of the triangle is 90 cm?

Answer 1

What we can do is set up an algebraic equation. 

our variable can me L for Length

3L+4L+5L=90

now all we have to do is solve

12L=90
----   ----
12      12

L=7.5

now multiple each number in the ratio by 7.5 to find out how long each side is

3 times 7.5 is 22.5
4 times 7.5 is 30
5 times 7.5 is 37.5

the side lengths are 22.5, 30, and 37.5