Manu uses only the digits 2 and 5 to make different three-digit numbers. For example, 252 and 222 are two possible numbers. What is the sum of all of Manu's possible three-digit numbers?

222 225 252 555 552 525 255 522 total 3108

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.

A five-digit number is formed using digits 1,3,5,8 and 9 without repeating any one of them. What is the sum of all such possible numbers?

There are four solutions.