I'm thinking of a number.
What is the number?
91 ===> 9 + 1 = 10. 91 - 72 = 19.
When a two digit number is multiplied by sum of its digits, the product is 715 but when the reverse of a two digit number is multiplied by sum of its digits the product obtained is 99 less. What is the sum of the digits of a number?
For some positive integer k both 4^k and 5^k start with the same digit x in base 10 i.e. 4^k = x..... 5^k = x..... What is the sum of all possible values of x.
