If A = {1, 2, 3, 4, 5}, how many two-element subsets does A have?
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Answer and explanation
Correct answer: 10
A two-element subset is formed by choosing any two different elements from the five elements of A, with order ignored. Thus the number is C(5, 2) = 5!/(2!3!) = (5 × 4)/2 = 10. For example, {1, 2} and {2, 1} represent the same subset, so they are counted only once. Hence option B is correct.
Frequently asked questions
What is the correct answer to this question?
10
Why is this the correct answer?
A two-element subset is formed by choosing any two different elements from the five elements of A, with order ignored. Thus the number is C(5, 2) = 5!/(2!3!) = (5 × 4)/2 = 10. For example, {1, 2} and {2, 1} represent the same subset, so they are counted only once. Hence option B is correct.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Power Set and Subsets.
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