Data VAlidation With If statement

Consider i have an amount e.g. 100,000 in A1. Now this amount can be divided equally on 24 months or 36 months i.e. 100,000/24 or 100,000/36.

I want to create formula that if i select 2 years in validation column( "A2" ) it Automatically divide the A1 value by relevant no of months and map the result monthly from January to December in appropriate columns. I have attached a sample file of what i want.

Please have a look.