Answer:
32
Step-by-step explanation:
You want the total number of questions on the test if the final score was 50%, and there were 13 correct out of the first 20, and 25% correct among the remainder.
Let q represent the number of questions on the test. Then (q-20) is the number of remaining questions, and the number correct is ...
13 +0.25(q -20) = 0.5(q)
8 +0.25q = 0.5q . . . . . . . simplify
8 = 0.25q . . . . . . . . . . . . subtract 0.25q
32 = q . . . . . . . . . . . . . . multiply by 4
There were 32 questions in total on the test.