There is only ½ of a whole cake How many pieces of cake have you and your friends eaten?

Answer 1

apparently you and your friends ate the 1/2 case that is missing

Full cake - half a cake = half a cake

how many pieces each ate depends on how many friend you shared the cake with, call it F

then F+1 = the number of pieces each ate. That's the number of Friends plus 1 where 1 represents You. That assumes "You" is singular, and not plural. In English "You" is ambiguous as to number.

Call it F+Y where F = number of friends and Y = number of "You," if there are more than one of "You."

Then there are F+Y pieces of cake that you shared. Each the size of 1/2 the cake = 1/(2F+2Y) in size