Randomising the chance that something will appear

Well as the thread title says, I need to randomise the chance that something will appear. I've done this before when I like say 2% of the time a bonus may appear, and that's fine. But now I need to say that something WILL appear but it will be one of 5 items. Each of those items has a predefined % chance that it will appear.

So for example:

A = 10%
B = 10%
C = 10%
D = 20%
E = 50%

Previously I've done things like populated and array with 1xA, 1xB, 1xC, 2xD, 5xE and then I've randomised a number from 1 to 10 and picked an array slot. That works fine, but if I want to use decimal places for my % chance then I'd have to make an array 1000+ or more slots long which is silly.

OK so I could do this:

1) Create a random number from 0 to 100.
2) Start a loop going and test if the random number is in the range of A, and if not check B and so on until E has been checked (well E does not need to be checked because if the random number is not in the range of D, we know it's in the range of E)

This seems a bit slow though, especially if I have LOTS of the items generating each logic loop.

Can anyone think of a quicker way? A Select Case would be pretty much the same as running a loop.

Thanks!