In a class of 42 students, 24 like mathematics, 18 like science, and 7 like both subjects. How many students like at least one subject?
Answer and explanation
Correct answer: 35
Let M be the set of students who like mathematics and S the set who like science. Students who like at least one subject belong to M ∪ S. By inclusion–exclusion, n(M ∪ S) = n(M) + n(S) − n(M ∩ S) = 24 + 18 − 7 = 35. The 7 students are subtracted once because they were counted twice.
Frequently asked questions
What is the correct answer to this question?
35
Why is this the correct answer?
Let M be the set of students who like mathematics and S the set who like science. Students who like at least one subject belong to M ∪ S. By inclusion–exclusion, n(M ∪ S) = n(M) + n(S) − n(M ∩ S) = 24 + 18 − 7 = 35. The 7 students are subtracted once because they were counted twice.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Operations on Sets (Union, Intersection, Difference).