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jmc

number theory senior

Problem

For how many integer values of between 1 and 474 inclusive does the decimal representation of terminate?
Solution
Recall that the decimal representation of a simplified fraction terminates if and only if the denominator is divisible by no primes other than 2 and 5. Prime factorizing 475 as , we see that terminates if and only if is divisible by 19. There are 24 multiples of 19 from 1 to 474, so there are possible values of that make a terminating decimal.
Final answer
24