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If C_r denotes the binomial coefficient C(15, r), find the value of the sum: C1/C0 + 2*(C2/C1) + 3*(C3/C2) +... + 15*(C15/C14).
- 100
- 120
- -120
- None
Correct answer: 120
Solution
Each term r*(C_r/C_(r-1)) = r*(16-r)/r = 16-r; summing from r=1 to 15 gives 15+14+...+1 = 120.
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