Suppose y varies directly with x, and y=15 when x=-5. Find x when y=18.

Answer 1

If y varies directly with x, we can write the equation as y = kx, where k is the constant of variation.

To find the value of k, we can substitute the given values of y and x into the equation. In this case, when y = 15 and x = -5:
15 = k(-5)
Dividing both sides by -5, we get:
k = -3

Now we can use the value of k to find x when y = 18. Substituting y = 18 and k = -3 into the equation:
18 = -3x

Dividing both sides by -3, we get:
x = -6

Therefore, when y = 18, x = -6.