CAT 1998 | Question: 92

Question

What is the digit in the unit place of $2^{51}$?

• A. $2$
• B. $8$
• C. $1$
• D. $4$

Answer 1

$2^{1}=2 \ ; \ 2^{2} = 4 \ ; \ 2^{3}=8 \ ;\ 2^{4}=16$

$2^{5}=32 \ ; \ 2^{6} = 64 \ ; \ 2^{7}=128 \ ;\ 2^{8}=256$

From above it is clear that the Cyclicity of 2 is 4.
 

$2^{51}=2^{48}\times 2^{3}$

Unit place of 48=6

Unit place of 49=2

Unit place of 50=4

Hence, unit place of $2^{51}=8$

 

Hence,Option(B)8.