In an examination, 30% of the total students failed in Hindi, 45% failed in English and 20% failed in both the subjects. Find the percentage of those who passed in both the subjects.

Let the number of students be 100. Number of students who failed in Hindi is 30%.
n(H) = 30
Number of students who failed in English is 45%.
∴ n(E) = 45
Number of students who failed in both the subjects is 20%. n(H ∪ E) = 20
Applying the rule,
n(H ∪ E) = n(H) + n(E) - n(H ∩ E)
= 30 + 45 - 20 = 55
Percentage of students who failed in Hindi or English or both the subjects = 55%
Number of students who passed in both the subjects = 100 - 55 = 45%