"I've always been 45 years older than your Dad", said Grandma to young grandson.

"But now the two digits in my age, both prime, are the reverse of the two in your Dad's age".

How old is Grandma?

If both digits are prime, the only available choices are 2, 3, 5, and 7. To add an odd mulitple of 5 to any number (ie, the number ends in 5), the ones digit of the sum will be either 5 higher or 5 lower than that of the other addend. It changes from 6 to 1, 2 to 7, 4 to 9, 9 to 4, etc. Therefore, the two digits must be 7 and 2. Since 72-27 is indeed 45, that is the solution.

Posted by DJ on 2003-03-01 09:53:12