Math CentralQuandaries & Queries


Question from Mike, a parent:

Every prime number larger than 10 has a digit in the ones place that is included in which set of numbers below?
A. 1,3,7,9
B. 1,3,5,9
C. 0,2,4,5,6,8
D. 1,3,7

Hi Mike,

Every integer with an even units digit is divisible by 2. Do you see why?

Every integer with a units digit of 5 is divisible by 5. Do you see why?

That leaves 1, 3, 7 and 9. Is there a prime number larger than 10 that has a units digit of 1? What about 3 and 7 and 9?


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