Q. The ten’s digit in $1! + 4! + 7! + 10! + 12! + 13! + 15! + 16! + 17!$ is divisible by
A) 4
B) $3!$
C) 5
D) 7
Explanation
(b)
As we know the last two digits of $10!$ and above factorials will be zero-zero
$\therefore\ \ \ 1! + 4! + 7! + 10! + 12! + 13! + 15! + 16! + 17!$
$= 1 + 24 + 5040 + 10! + 12! + 13! + 15! + 16! + 17!$
$= 5065 + 10! + 12! + 13! + 15! + 16! + 17!$in this series, the digit in the ten palce is 6 which is divisible by $3!$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.