Q. $\ ^{20}C_{4} + 2 \bullet \ ^{20}C_{3} + \ ^{20}C_{2} - \ ^{22}C_{18}$ is equal to
A) 0
B) 1242
C) 7315
D) 6345
Explanation
(a)
Given, $\ ^{20}C_{4} + \ ^{20}C_{3} + \ ^{20}C_{3} + \ ^{20}C_{2} - \ ^{22}C_{18}$
$= \ ^{21}C_{4} + \ ^{20}C_{3} + \ ^{20}C_{2} - \ ^{22}C_{18}$
$= \ ^{22}C_{4} - \ ^{22}C_{18} = \ ^{22}C_{18} - \ ^{22}C_{18} = 0$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.