Question

Johnny has graded 20% of his 150 students papers how many papers does he still need to finish grading ?

Answer 1

The correct answer is 120 papers.

Answer 2

First change 20% to a decimal 20% = .20
Then you multiply 150x.20=30 to find out how many papers he has graded so far. 
Then subtract 30 from 150 to find out how many papers he still needs to grade.
150 - 30 = 120
So he has 120 papers left to grade.