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.

The overall percentage of increase of students for this middle school is about 17.2%

To do this you have to know the number of students in each grade and add them together and do this:

390 x 0.1 = 39 Students

350 x 0.22 = 77 students

420 x 0.2 = 84 students

Add all the number of students and do this:

(200 students over 1,160) x 100%

(Increased students over original students) x 100%

0.172 x 100% = 17.2%

The percentage increase of the students of the middle school is about 17.2%