Question

If y varies directly with x and y is 9 when x is 5, what is x when y is -1

Answer 1

x = -0.56

Explanation:

if y varies directly with x

i.e

y ∝ x

y= kx

where k is the constant of variation

when y is 9 and x is 5

9= 5k

k =9/5

k=1.8

when y=-1

then

-1=kx

-1=1.8x

x= -0.56

Answer 2

We use the fact that y = kx, where k is the constant of proportionality.

9 = 5k

9/5 = k

Now that we know k, we can find x when y = -1.

-1 = x(9/5)

-1/(9/5) = x

-5/9 = x

Did you follow?