Answer: 20.
- A 15
- B 30
- C 10
- D 20
Correct answer: D. 20
Explanation: 6C3 = 6!/(3! x 3!) = 720/(6 x 6) = 20.
Row n of Pascal's triangle gives the coefficients nC0, nC1, ..., nCn for the expansion of (a+b)ⁿ; each number is the sum of the two numbers diagonally above it, a direct visual proof of the identity nCr = (n-1)C(r-1) + (n-1)Cr.
Concept context
Expansion of (a+b) n , general term, middle term, binomial coefficients, and greatest term