2017 AMC 8 Problems/Problem 14

To solve this problem, first substitute the amount of problems as 100. This means that 50 of the problems were solved alone. 80% of 50 is 40. This means that 48 of the problems were solved together. 90% of 50 is 45. This means that 45+48, so (C) percent of Zoe’s problems were correct.

~pegasuswa