The sum of all integers from 1 to 520 which are multiples of 4 or 5 is:

The sum is 54,340. Inclusion–exclusion gives $4(1+\cdots+130)$ $+5(1+\cdots+104)$ $-20(1+\cdots+26)$. Thus the total is $34{,}060+27{,}300-7{,}020$ $=54{,}340$, subtracting multiples of 20 because they were counted twice.