Question

What is the value of `x` in the equation `1/5x -2/3 y=30,` when `y=15`?

Answer 1

`x = 200`

Explanation:

Okay so we can start by substituting in `y` as we know what it is already:

`(1/5)x - (2/3)(15) = 30`
Now at this stage we could use a calculator to figure out what `2/3` of `15` are though a bit of mental math is as easy:

`(15/3) * 2 = 5 * 2 = 10` (the dots mean multiply)

okay so now we have:

`(1/5)x - 10 = 30` add 10 to both sides to get rid of the `-10`

`(1/5)x = 40` let's get rid of that fraction by multiplying by `5`

`x = 200` and there's the solution for x

We can check we got this right by substituting it back into the original equation with the known y:

`(1/5)(200)-(2/3)(15) = 30`

now `200 / 5 = 40` and we already know what `2/3` of `15` is so :
that means

`40 - 10 = 30` which is ✓

Therefore we know our solution is right.