IMAS 2020–2021 Junior Division — First Round Question 16

Question 16

Using the numbers $1,2,\ldots,2020$, let the sum of all the numbers that are divisible by 3 be $X$ and the sum of all the numbers that are divisible by 2 but not by 3 be $Y$. What is the value of $X-Y$?

$1008$
$-1008$
$1344$
$1011$
$-1011$