A set has 63 proper subsets. How many elements are in the set?
If a set has 63 proper subsets, we can use the formula for calculating the number of subsets of a set with n elements, which is 2^n.
Since the question specifies that the set has proper subsets, we need to subtract the empty set from the total number of subsets.
So, 2^n - 1 = 63
2^n = 64
n = 6
Therefore, the set has 6 elements.