Project Euler : Problem 1

Problem

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If we list all the natural numbers below $10$ that are multiples of $3$ or $5$, we get $3, 5, 6$ and $9$. The sum of these multiples is $23$.

Find the sum of all the multiples of $3$ or $5$ below $1000$.

Solution

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Explaination

Add up all the multiples of 3 less than 1000. Add to this all the multiples of 5 to this number. Subtract all the multiples of 15 from this number.