Question

Find the sum of first 12 natural numbers without using the formula or by adding terms directly.

• A. 58
• B. 78
• C. 48
• D. 98

Answer 1

The correct option is B

78

The first 12 natural numbers are 1,2,3,4,5,6,7,8,9,10,11,12.

Let the sum be "s"

s=1+2+3+4+5+6+7+8+9+10+11+12...................(1)

We can rewrite "s" as below:

s=12+11+10+9+8+7+6+5+4+3+2+1...................(2)

Add the equations (1) and (2).we get ..

2s=13+13+13+13+13+13+13+13+13+13+13+13

$\Rightarrow 2s=13\times 12$

$\Rightarrow 2s=156$

$\Rightarrow s=\frac{156}{2}$

$\Rightarrow s=78$