Question

What is the value of x in the equation 3x-y = 30, when y = 15?

Answer 1

`x=200`

Step-by-step 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`

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`

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, and we already know what out of is so :

that means

which is ✓

Therefore we know our solution is right.

Answer 2

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