Question

How do you solve by substitution `m + n = 5` and `m – n = 3`?

Answer 1

First solve one variable in terms of the other.

Explanation:

`m-n=3` add `n` on both sides:
`m=n+3`

Now substitute this for `m` in the other equation:
`(n+3)+n=5->2n+3=5->n=1`

Then use this to find `m`:
`m=n+3=1+3=4`

Or:
`m+n=5->m=5-n->`
`(5-n)-n=3->5-2n=3->-2n=-2->n=1->m=5-1=4`
Or:
`m+n=5->n=5-m->`
`m-(5-m)=3->m-5+m=3->2m=8->m=4->n=5-4=1`