Question

How do you solve `x=y+4` and `5x+3y=-20` using substitution?

Answer 1

`y = -5`
`x = -1`

Explanation:

First we substitute in our value for `x` (which is `y+4`) into the other equation so that we only have one unknown, `y`.
Then you expand the bracket and simplify it to find `y`.

`5x+3y = -20`
`5(y+4)+3y=-20`
`5y + 20 +3y= -20`
`8y+20=-20)`
`8y = -40`
`y=-40/8`
`y=-5`

Now we use our value for `y` in the original equation to find `x`.

`x = y+4`
`x = -5+4`
`x=-1`

We can then check our answer by substituting both values into the other equation:

`(5xx-1)+(3xx-5) = -20`
`-5+ (-15) = -20)`
`-5 - 15 = -20`
`-20 = -20`
So we know it's right!
It's really important to check your answers, as in a test, it could save you a whole load of marks despite only taking a few seconds:)

Hope this helps; let me know if I can do anything else:)