front-ended back ended volume scenarios

Hello. I have 30 days in a month. I want to create a couple of scenarios that I can switch easily (i.e. not inserting manually). Here they are 1) Lots of volume in the beginning of the month 2) Lots of volume at the end of the month 3) even volume

Can someone give me a way I can create this scenario and then change the values of the cells by choosing 1,2, 3?

Thanks!!