If a two digit number is not divisible by (), then it must be prime Ask which teacher to help answer, the answer has been known, but I do not know why, for the analysis process. Thank you!

If a two digit number can not be divided by (2,3,5,7), then the two digits must be prime numbers. ∵ the maximum number of two digits is 99. If it is a composite number, there must be a factor less than √ 99 = 9.9.. if it is a factor greater than 9, then it should be a number with three or more digits. ∵ if a two digit number cannot be divided by (2,3,5,...)

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