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Printsmc
number theory intermediate
Problem
Find the sum of all prime numbers between and that are simultaneously greater than a multiple of and less than a multiple of .
(A)
(B)
(C)
(D)
Solution
Numbers that are less than a multiple of all end in or . No prime number ends in , since all numbers that end in are divisible by . Thus, we are only looking for numbers that end in . Writing down the ten numbers that so far qualify, we get . Crossing off multiples of gives . Crossing off numbers that are not more than a multiple of (in other words, numbers that are less than a multiple of , since all numbers are odd), we get: Noting that is not prime, we have only and , which give a sum of , so the answer is .
Final answer
A