Puzzle-6 (CAT-2005)

The right most non zero digit of the number 302720  is 

(A)1      (B) 3     (C) 7     (D) 9          

Solution follows here:

Solution:

30²⁷²⁰ = 3²⁷²⁰ * 10²⁷²⁰

As 10²⁷²⁰ produces all zeroes from right side, the last digit (unit digit) of 3²⁷²⁰

is the right most non zero digit of 30²⁷²⁰.

To find the unit digit of 3²⁷²⁰:

(Please refer to “Magic of Numbers-1(unit digit...)” post of this blog)

As 2720 is multiple of 4, we consider 4^th digit of the unit digit pattern of 3ⁿ.

The unit digit pattern of 3ⁿ is 3,9,7,1

Answer is (A)