Question 18
How many 3-element subsets {a,b,c} of {1,2,...,100} have the property that a+b+c is a multiple of 6? For example, {1,2,3} and {2,6,10} are examples of such sets.
(Note: {a,b,c}, {a,c,b} and {b,a,c} are considered as the same set.)
(Note: {a,b,c}, {a,c,b} and {b,a,c} are considered as the same set.)