Question

If y varies inversely as x, and y=10 when x=4, how do you find x when y=8?

Answer 1

`x=5`

Explanation:

`y prop 1/x :. y=k*1/x :. x*y =k ;`

When `x=4 ; y=10 :. 4*10=k or k=40`.

So variation equation is `x*y =40`

When `y=8 ; x=40/8=5 :. x=5` [Ans]

Answer 2

`x=5`

Explanation:

`"the initial statement is "yprop1/x`

`"to convert to an equation multiply by k the constant"`
`"of variation"`

`rArry=kxx1/x=k/x`

`"to find k use the given condition"`

`y=10" when "x=4`

`y=k/xrArrk=yx=10xx4=40`

`"equation is " color(red)(bar(ul(|color(white)(2/2)color(black)(y=40/x)color(white)(2/2)|)))`

`"when " y=8`

`x=40/y=40/8=5`