If U = {a, b, c, d}, how many elements of P(U) have a singleton complement?
Answer and explanation
Correct answer: 4
Let S be a subset of U. If its complement U − S is a singleton, then exactly one element of U is outside S, so S must contain exactly three elements. The number of three-element subsets of a four-element set is C(4,3) = 4. Therefore, exactly four elements of P(U) have singleton complements.
Frequently asked questions
What is the correct answer to this question?
4
Why is this the correct answer?
Let S be a subset of U. If its complement U − S is a singleton, then exactly one element of U is outside S, so S must contain exactly three elements. The number of three-element subsets of a four-element set is C(4,3) = 4. Therefore, exactly four elements of P(U) have singleton complements.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Power Set and Subsets.