The positive integers 1 through 49 are divided into k disjoint subsets so that no two integers whose sum is divisible by 10 are in the same subset. For example, 13 and 37 cannot be in the same subset. What is the smallest possible value of k?
@guest, next time, please try to include an explanation.
As you see, if you google, this, ANOTHER PERSON WHO DIDN"T CARE TO GIVE AN EXPLANATION EVEN WHEN THE ASKER SAID SO said the answer was 11. SO WHICH ONE IS RIGHT? Now they don't know.
