Generate random number in range [M....N] with mean X

Generating a random number in the range [M..N] is easy enough. I however would like to generate a series of random numbers in that range with mean X (M < X < N).

For example, assume the following: M = 10000 N = 1000000 X = 50000 I would like to generate (a large amount of) random numbers such that the entire range [M..N] is covered, but in this case numbers closer to N should become exceedingly more rare. Numbers closer to M should be more common to ensure that the mean converges to X.

The intended target language is PHP, but this is not a language question per se.