Explanation:
part A has 20 questions.
20% are correct, that means
100% = 20
20% = 100%/5 = 20/5 = 4
so, she has 4 questions correctly answered in part A.
she needs 15 correctly answered questions in total.
therefore, she needs to answer 11 questions correctly on part B.
part B has also 20 questions. how many % are 11 questions ?
100% = 20
1% = 100%/100 = 20/100 = 0.2
11 are a many % as 1% fits into 11 :
11/0.2 = 55
she needs to answer 55% of the questions correctly in part B.