+56 Let S be a set of distinct integers. What is the smallest number of elements that S must contain, to ensure that S has a nonempty subset, where the sum of the elements in the subset is divisible by 2?
+4 If the set has only 1 odd number, its sum will be odd — not divisible by 2. But as soon as there are 2 numbers in the set (whether 2 odds or one even), then some subset will have an even sum.
So, the minimum number of elements needed in the set to guarantee a non-empty subset with a sum divisible by 2 is 2.
Answer: 2
