Question

How do you work out this equation?

solve simultaneous equations by substitution
x + y =3
5x + y = 15

Answer 1

Explanation:

x+y=3

5x+y = 15

I method:

y = 3 - x. substitute this in 2nd equation

5x + (3-x) = 15

5x + 3 - x = 15

4x = 12

x=3

y=0

II method:

subtracting 2nd equation and 1st equation we get

4x +0y = 12

x = 3

y = 0

Answer 2

Explanation:

x + y = 3. => y = 3 - x

5x + y = 5x + (3 - x) = 15.

=> 4x + 3 = 15

=> 4x = 12, x = 3.

Therefore y = 3 - (3) = 0.

The solutions are x = 3 and y = 0.