I've been trying for 3 hours and still can't get the hang of it!!

Question

At a certain middle school, the 6th-grade class of 390 increased by 10%, the 7th-grade

class of 350 increased by 22% and the 8th-grade class of 420 increased by 20%.

Overall, what was the percentage increase of students for this middle school? Express

your answer to the nearest tenth.

Answer 1

Number of students in middle school before the increases = 1160

Number of students in 6th grade after a 10% increase = 390 + 0.10(390) = 429

Number of students in 7th grade after a 22% increase = 350 + 0.22(350) = 427

Number of students in 8th grade after a 20% increase = 504

Total number of students in middle school after the increases = 1360

Percent increase = [(1360 - 1160) / 1160] (100) ≈ 17%