Question

Find the sum of first 100 even natural numbers which are divisible by 5.

Answer 1

The numbers are 5,10,15...and so on are natural numbers.
Even natural numbers will be 10,20...and so on
Since they are in AP with common difference =10

No. of terms = 100

$S_n$= $\frac{n}{2}$ ($2a+(n-1)d$)

$S_n$ = $\frac{100}{2}$ [$2\times 10+(100-1)10$]

$S_n$ = 50 $\times$ [20 + 990]

$S_n$ = 50 $\times$ 1010

$S_n$ = 50500