So far, you have 80% of the 75% of the total points for the class. To get greater than or equal to 72% of the 100% of the points for the class, you will need:

(80/100)(75/100)T + (x/100)(25/100)T = (72/100)T [T=total points; x=score on last essay]

(80)(75/100) + (x)(25/100) = 72 [multiply all terms by 100/T]

6000 + 25x = 7200 [multiply everything by 100]

25x = 1200 [subtract 6000 from both sides]

** x = 48 ** [you only need a 48 to get a class average of 72]

Bob J.

11/17/15