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Grandma was 72 years old. Let the two digits be A and B. Then 10A+B-10B-A=45 so 9(A-B)=45. This gives A-B=5. Of the pairs 5,0; 6,1; 7,2; 8,3; 9,4 only 7,2 are both prime numbers.

The answer to yesterday’s riddle is that Mount Everest has always been the tallest. Even before it was discovered. Whitey was the first to respond correctly. Steven was the first to show that he is a product of the public school system. Riddle #3 “I’ve always been 45 years older than your Dad”, said Grandma.” [...]