If A = {1, 2, 3, 4}, how many subsets in P(A) have at least three elements?
Answer and explanation
Correct answer: 5
At least three elements means that a subset may contain exactly three elements or exactly four elements. The number of three-element subsets is C(4,3) = 4, and the number of four-element subsets is C(4,4) = 1. Adding them gives 4 + 1 = 5. Hence option B is correct; counting only three-element subsets would miss A itself.
Frequently asked questions
What is the correct answer to this question?
5
Why is this the correct answer?
At least three elements means that a subset may contain exactly three elements or exactly four elements. The number of three-element subsets is C(4,3) = 4, and the number of four-element subsets is C(4,4) = 1. Adding them gives 4 + 1 = 5. Hence option B is correct; counting only three-element subsets would miss A itself.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Power Set and Subsets.