JEE PYQ: Binomial Theorem Question 22
Question 22 - 2020 (04 Sep Shift 1)
The value of $\sum_{r=0}^{20} {}^{50-r}C_6$ is equal to:
(1) ${}^{51}C_7 - {}^{30}C_7$ (2) ${}^{50}C_7 - {}^{30}C_7$ (3) ${}^{50}C_6 - {}^{30}C_6$ (4) ${}^{51}C_7 + {}^{30}C_7$
Show Answer
Answer: (1)
Solution
Hockey stick identity: ${}^{50}C_6 + {}^{49}C_6 + \ldots + {}^{30}C_6 = {}^{51}C_7 - {}^{30}C_7$.