Q. If $\ ^{8}C_{r} - \ ^{7}C_{3} = \ ^{7}C_{2}$, then $r$ is equal to
A) 3
B) 4
C) 8
D) 6
Explanation
(a)
Given ,
$\ ^{8}C_{r} - \ ^{7}C_{3} = \ ^{7}C_{2}$
$\Rightarrow \ ^{8}C_{r} = \ ^{7}C_{3} + \ ^{7}C_{2}$
$\Rightarrow \ \ ^{8}C_{r} = \ ^{8}C_{3}$
$\Rightarrow r = 3$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.