Hi I am trying to work out which seems to be an obvious fact but can't see it!

Let A be a set s.t. A = {x: y(x) < k(x)/p}. Then u(A) = measure of A >= (1-p).

Note 0<p<1.

The functions are defined as follows:

y(x) is a random variable

k(x) is the mean of the random variable y(x)

Thank you!