Each digit of a 9-digit number is 1. It is multiplied by itself. What is the sum of the digits of the…

Each digit of a 9-digit number is 1. It is multiplied by itself. What is the sum of the digits of the resulting number?
  1. 64
  2. 80
  3. 81
  4. 100

Solution

The repunit 111111111 (nine 1's) squared gives 12345678987654321. The sum of its digits is $1+2+3+4+5+6+7+8+9+8+7+6+5+4+3+2+1 = 81$.

Asked in: CSAT 2023

Practice more General Mental Ability questions on Aicharya