How to create random character strings with proportional distribution?

please somebody could help me. In this case i want to create a proporsional distribution of random character within Ms. excel cells e.g.35 column to fill with a a-e character. The previous i create with following code:

=CHAR(RANDBETWEEN(65,69))

and resulting the following figure:

but, it isnt create a proportional number of alphabet distribution e.g a must be 7, b must be 7, etc..

Please someone help me. Thank you.