Suppose that y varies inversely with x. write an equation for the inverse variation.
y = 4 when x = 7

If y varies inversely as x, then we write it as:
y = k/x

where k is some constant.

If we multiply both sides of this equation by x we get an equation for k:
k = x*y

We are given that y=4 when x=7, therefore:
k = 7*4 = 28

Put this back into our original equation to get:
y = 28/x