Question

Find the sum of the first 100 natural numbers.

Answer 1

$S_n=1+2+3+...100$

$S_n=100+99+...+1$

Add both $e{q}^n$

${25}_n=101+101+...+101$

$100$ times

$\Rightarrow {25}_n=101\times 100$

$\Rightarrow S_n=5050$