Question

Find the sum of the first 18 natural numbers.

• A. 171
• B. 161
• C. 191
• D. 181

Answer 1

The correct option is A

171

The first 18 natural numbers are 1,2,3,... and 18.

The sum of the first $n$ natural numbers is given by

$S=1+2+3+...+n=\frac{n\times (n+1)}{2}.$

Here, $n=18.$

$\therefore S=\frac{18\times (18+1)}{2}$

$=\frac{18\times 19}{2}$

$=\frac{342}{2}=171$

Thus, the sum of the first 18 natural numbers is 171.