If y varies directly with x, and If y = -36 when x = 6, how do you find x when y = 42?

1 Answer
May 25, 2017

x=-7

Explanation:

If y varies directly with x that means:

y=kx

where k is a constant.

When we say a variable varies directly with another variable, that is another way of saying that if the first variable increases, the second variable increases and vice-versa.

Now, we simple solve for k and substitute the values of x and y to find the constant k.

k=y/x

k=(-36)/6

k=-6

To find x when y=42, we will solve for x in the original equation and substitute the values of k and y.

y=kx

x=y/k

x=42/-6

x=-7