Project Euler: Problem 1 (Possible refactorings and run time optimizations)

Question

I have been hearing a lot about Project Euler so I thought I solve one of the problems in C#. The problem as stated on the website is as follows:

If w

Answer 1

new List<int>{3,5}.SelectMany(n =>Enumerable.Range(1,999/n).Select(i=>i*n))
                  .Distinct()
                  .Sum()

[Update] (In response to the comment asking to explain this algorothm) This builds a flattened list of multiples for each base value (3 and 5 in this case), then removes duplicates (e.g where a multiple is divisible, in this case, by 3*5 =15) and then sums the remaining values. (Also this is easily generalisable for having more than two base values IMHO compared to any of the other solutions I have seen here.)