The final grade for a particular course is calculated by dividing total points earned by total points available. There are 120 points available in the first half of the course, and 140 points in the second half of the course. If a student earns 81% in the first half of the course, how many points must the student earn in the second half in order to earn an 80% B final grade?

Answer 1

120 * 0.81 = 97.2

260 * 0.8 = 208

208 - 97 = 111

Answer 2

There are 2 halves in the course:
1st half has 120 points
2nd half has 140 points
-- for a grand total of 260 points

If a student earns 81% of the points in the 1st half, she earns 0.81 * 120 points
-- 0.81 * 120 = 97.2 points

If there are 260 total points in the class, and the student wants to earn a B final grade, that is 0.8 * 260 points
-- 0.8 * 260 = 208 points

208 - 97.2 = 110.8 points
-- the student still needs 110.8 or 111 points from the second half