Brain food

stock math

Problem
Find the sum of all the multiples of 3 or 5 below 1000. For example; sum of all natural numbers less than 10, that are multiples of 3 or 5 (3, 5, 6, & 9), is 23.

Solution
lbrace xverthspace{2 mm} 1leq xleq 1,000rbrace If there’s no remainder when x is divided by 3 or 5, take the sum of all those x’s.


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Food for thought. Or not.