Generate Random numbers where sum = 1

Hi, currently I have 3 cells where I would like to generate randomn numbers so that the sum of these cells = 1 (or 100%). Is there a way of doing this. Also currently I have 3 cells, but would like to have a function where I can apply to it X number of cells. Any help will be much appreciated. Thanks

in A1:
=rand()
in A2:
=rand()*(1-A1)
in A3:
=1-A1-A2

As you add more numbers you run into issues with how random the numbers are, you will always have a distribution as to where the numbers fall, i.e. you will have many more low numbers than you have high numbers. You need to assign some sort of weighting function/curve to determine the distribution.

See the discussion in this thread which is very similar to your problem:
http://www.excelforum.com/excel-gene...in-number.html