Quandaries
and Queries |
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The units digit of a two-digit prime number is not greater than the tens digit by 3.If the positions of the two digits are interchanged, then the new number formed is greater than the original number by more than 18. Find the value of the original prime number. |
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Hi, I would first write a column of the two digit primes, perhaps using the Sieve of Erathosthenes. Strike out the numbers in your list which have the units exceeding the tens digit by more than 3. Beside each of the numbers that remain write the number obtained by reversing its digits. Look down the list to find any where the new number formed is greater than the original number by more than 18. Penny |