How to solve this question?I need step by step solution.
If 75% of the students were able to answer the first question correctly, 55% were able to answer the second question correctly and 20% answered both the questions wrong.
What percentage of students answered both the questions correctly?

Answer is 50%. It can be calculated simply by breaking down the problem.

Say we have 100 students.
75 of them got the first question right, 25 got it wrong.
55 got the second question right, 45 got it wrong.
20 got both wrong which means 80 got either both or at least on question right.

Now, we know that 25 students got Q1 wrong, out of those 25, 20 also got Q2 right. So we have only 5 students who only answered the Q1 incorrectly. We also know that 45 students got Q2 wrong, 20 of those 45 also got Q1 wrong, so we have 25 students who only answered the second question incorrectly.

We also know that 80 students answered either both or at least one of the two questions correctly. To get the students with two correct answers, we simply subtract the number of students who got one of the two questions wrong from 80. Now we know that 5 students only got Q1 wrong so we subtract 5. We also know that 25 students only got Q2 wrong, so we subtract 25 too. The number of students we're left with is 50. This is the number of students who got both answers right.