Brain Teasers
Grandma's Age
"I've always been 45 years older than your Dad", said Grandma to young Trickle. "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?
Answer
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.Hide Answer Show Answer
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Comments
Nice teaser! Don't forget the 2 being a prime.
btw, how old was trinkle to figure all this out
who has a kid at age 45
Trickle's grandmother does, Triskit.
Easy if you remember that 2 is prime, so you can see that for the trick.
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