Changing Data Based on Drop Down Box Selection

Hello
I could use some help with changing the data based on a drop down selection.
My drop down list is based on the months I need the data (percentages for each person) to change depending on which month is chosen
So If I select Jan, the percentage fills in for each person.

I've attached an example. If someone could help, I wold really appreciate it.

Thanks!

Thank you but I can't get it to change the values of the whole row of people, only the first one. So of I select
"March", John's percentage changes to .30 but that's the only one that changes. Do I need to put the formula somewhere particular to change the rest of the people? I'm not very good at this when it comes to all the formulas.

Thanks!

I figured it out my second problem Thank you so much for your help!!