Conditional Formula help please

Hello everyone! :)

Let me both thank everyone in advance for any help received and also apologize as I think I only know enough about excel formulas to be just a little dangerous (so to say).

I am trying to create a conditional formula. I was able to create the two formulas that are needed but I have no idea/clue how to have it do what I am looking to do. I am puzzled. What I am trying to do is (hope I explain this correctly) if cell B20 is <1 have it take cell a20 and multiply it by F20 but if Cell B20 is >0 then it subtracts cell b20 from a20 and then multiplies that by F20. I believe I came up with the formulas for each, but I am unsure how to have it all in one formula as a conditional..Any help is greatly appreciated! Thank you in advance. Andy Happy 4th to all in the US.

=SUM(B20<1)*(A20*F20)
=IF(B20>0,IMSUB(A20,B20)*F20)

completing the IF statement

I am a little confused as you state do something if it is greater than 0, but you also state to do something else if it is less than 1. 0.5 is both greater than 0 & less than 1

the below will multiply A20 with F20 for any value <=0
=IF(B20>0,IMSUB(A20,B20)*F20,A20*F20)

If you want something else can you please clarify your conditions a bit more?

Regards
Mark