ans is D. 80 questions
explaination
there are multiple ways to solve this question.
one is simple
assume total question is x
20% of x = 16
20/100 × X = 16
solve for x and you will get 80.
another one is because 16 represents only 20% , so lets calculate how many such part required to make it 100.
100/20 = 5 times
so we need to multiply 16 with 5 which gives us 80.
take another example . if 25 % of total question is 8. then what is total no of questions.
same way
total part = 100/25 = 4 times
so 8 × 4 = 32 questions. this approach is to solve if given percentage is simple one to make quick solution.