1. Tardigrade
  2. Question
  3. Mathematics
  4. The value of r for which 20Cr 20C0 + 20Cr-1 20C1 + 20Cr-2 20C2 + .... 20C0 20Cr is maximum, is

Question Error Report

Thank you for reporting, we will resolve it shortly

Back to Question

Q. The value of $r$ for which ${^{20}C_r} {^{20}C_0} + {^{20}C_{r-1}} {^{20}C_1} + {^{20}C_{r-2}} {^{20}C_2} + .... {^{20}C_0} {^{20}C_r}$ is maximum, is

JEE MainJEE Main 2019Binomial Theorem

Solution:

Given sum = coefficient of $x^r$ in the expansion of $(1 + x)^{20} (1 + x)^{20}$, which is equal to $^{40}C_r$
It is maximum when $r = 20$