Browse · MATH
Printjmc
number theory senior
Problem
Let be the set of all integers such that, if is in , then and are terminating decimals. What is the smallest integer in that is greater than 2010?
Solution
Let us first analyze the fraction . We can rewrite this fraction as . Since the denominator can only contain powers of 2 and 5, we have that must be a multiple of 33. We now continue to analyze the fraction . We rewrite this fraction as , and therefore deduce using similar logic that must be a multiple of 21. From here, we proceed to find the least common multiple of 21 and 33. Since and , we conclude that the least common multiple of 21 and 33 is .
We now know that contains exactly the multiples of 231. The smallest multiple of 231 that is greater than 2010 is .
We now know that contains exactly the multiples of 231. The smallest multiple of 231 that is greater than 2010 is .
Final answer
2079