Subject: General Aptitude · Chapter: Number System · Exam: · Marks: · Difficulty:
Unit's digit in $(784)^{126}+(784)^{127}$ is
(a)0
(b)4
(c)6
(d)8
Answer
Answer (as printed): A
Explanation
Unit digit of $4^{2}$ is 6. So, unit digit in $\left(4^{2}\right)^{63}$ is 6 . ∴ Unit digit of (784) ${ }^{126}=$ Unit digit in $4{ }^{126}$, which is 6. Unit digit in $4^{127}=$ Unit digit in $\left(4^{126} \times 4\right)=$ Unit digit in $(6 \times 4)$, which is 4. ∴ Unit digit in (784) ${ }^{127}$ is 4. Hence, unit digit of $\left\{(784)^{126}+(784)^{127}\right\}=$ Unit digit of $(6+4)=$ Unit digit of 10 , which is 0 .
Explanation as extracted from the printed page; notation may be imperfect.