The value of 100C5051 + 100C5152 + + 100C100101 is:
- 2101101
- 2100101
- 2100100
- 2101100
Answer
(2) 2100101
Solution
nCrr + 1 = n+1Cr+1n + 1
100Crr + 1 = 101Cr+1101
S = 1101 (101C51 + 101C52 + + 101C101 )
Since 101Ck = 101C101-k, the terms k = 51 to 101 are exactly half of all the coefficients:
101C51 + + 101C101 = 21012 = 2100
S = 2100101
Answer: (2)