So I have the values 45 through 90. I can easily generated a number in that range with RANDBETWEEN(45,90)

What I want to do is generated a random number in that range with the probability of it being within a smaller range inside.

I want the number to fall between 45-90 with the following probabilities;

45-50 = 10%
51-65 = 30%
66-75 = 50%
76-90 = 10%

Anyone know how to do this easily?