Question

How do you solve the system of equations `b= \frac { 3} { 4}a` and `a + b = 21`?

Answer 1

`a=12` and `b=9`

Explanation:

As `b=3/4a`, putting this value of `b` in `a+b=21`, we get

`a+3/4a=21`

or `7/4a=21`

or `7/4xx4/7a=21xx4/7`

and `a=21xx4/7=cancel21^3xx4/cancel7^1=12`

and `b=3/4xx12=3/cancel4^1xxcancel12^3=9`