Question

Find the sum of the first ten multiples of $5$.

Answer 1

Sum of the first ten multiples of $5$

$5+10+15+.....+50$

$5(1+2+3+...\dots +10)$

$1+2+3+4+5+6+7+8+9+10=\frac{10\times (10+1)}{2}=5\times 11=55$

$\therefore$ Sum of the first ten multiples of $5$ is $5\times 55=275$.