CA Foundation · Quantitative Aptitude · Permutations and Combinations
What is the value of 12C4 + 12C5?
The value is 1287. Using Pascal's rule, 12C4 + 12C5 = 13C5, which equals 1287. Directly, 12C4 = 495 and 12C5 = 792, and their sum is also 1287.
- A792
- B1287Correct
- C495
- D1320
Explanation
By Pascal's rule, nCr + nC(r+1) = (n+1)C(r+1), so 12C4 + 12C5 = 13C5. 13C5 = (13×12×11×10×9)/120 = 154440/120 = 1287. Check: 495 + 792 = 1287. Option 792 is only 12C5.
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