[administration]

Q. Define A= the sum of digits of the number 7^100 and B= The sum of digits of A. What is the sum of digits of B?
7
16
10
CBD!

[Wonder Boy]

Digital Sum Rule of Multiplication says : The digital sum of the product of two numbers is equal to the digital sum of the product of the digital sums of the two numbers.

 

so 7³ = 343

so sum of digits of 7³ = 3+4 +3 = 1+0 = 1

–> sum of  digits of 7¹⁰⁰ = sum of digits (7)⁹⁹.7 = sum of digits of (7³)³³.7 = sum of digits of (1)³³.7 = 7 Ans

 

[Author]

Posts