Hi Alyssa,

Think of the total grade being a possible 100 points. So far you have 65% of a possible 80 points and there are a possible 20 more points on the upcoming exam. 65% of 80 is 0.65 × 82 = 52 and thus you have 52 of a possible 80 points. To obtain an average in the course of 75% you need a total of 75 points. You have 52 already so you need 75 - 52 = 23 points. But there are only 20 points on the exam so you can't get an average of 75%. If you write a prefect exam you get 20 points giving you 52 + 20 = 72 points and thus 72%.

Penny