FORMULA HELP

[cONfUSEd LADY]

HI, MY PROBLEM IS THAT I NEED TO TAKE OFF 20% OF A SUM OF AN AMOUNT
EXAMPLE:
THIS IS THE SUM FORMULA =SUM(C1:C15)
BUT WHEN I PUT =SUM(C1:C15) - 20% DONT MAKE ME THE CORRECT RESULT
SUPOSSED TO THE SUM IS EQUAL TO $22.01 THE CORRECT 20% OF IS $4.40, BUT WHEN
I PUT THE FORMULA =SUM(C1:C15) - 20% THE RESULT THAT EXCEL GAVE ME WAS $
21.81 THAT'S NOT CORRECT THE CORRECT AMOUNT IS $17.60, PLEASE CORRECT ME IF
IM MAKING A WRONG FORMULA OR PLEASE TELL ME WHAT KING OF FORMULA I NEED TO
USE.

THANKS

 

[evilthorne]

=SUM(C1:C15)*(1-20%)