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

Question

21108 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2016-06-25T17:40:51

$x = 200$

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.

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