Question

How do you solve by substitution `x + y = 11` and `x - y = 1`?

Answer 1

The first step would be to write `x-y=1 rarr x=1+y`
and then to replace `x` by `1+y` in `x+y=11`

thus `1+y+y=11 rarr 2y+1=11 rarr 2y=10 rarr y=5`

Now back to `x-y=1` with `y=5`

`x-5=1 rarr x=6`