Question

Find the units digit of the expression ${11}^1+{12}^2+{13}^3+{14}^4+{15}^5+{16}^6.$

• A. 1
• B. 9
• C. 7

Answer 1

The correct option is B 9

1, 5 and 6 raised to any power always end in 1, 5 and 6 respectively as their units' digit. For 2 & 3, the cyclicity is 4 and for 4, the cyclicity is 2. Hence, the respective units digits for the six parts of the expression would be:$1+4+7+6+5+6=29\to$ required answer is 9. Option (b) is correct.