BLANK CELL

[MAX]

I am using a formula in cell G1 and putting the quantity in cell F1 (
quantity never exceeds 20) but when cell F1 is blank the result in G1 becomes
50.
I want that when F1 is blank, the result in G1 becomes ZERO.
This is the formula that I am using:

=MIN(A1,MAX(10,10-A1))*5+MIN(20-10,MAX(0,A1-10))*4

Thank you for your help.

 

[Joel]

=if(F1="",0,MIN(A1,MAX(10,10-A1))*5+MIN(20-10,MAX(0,A1-10))*4)