Question

find the value of 1+2+3+.......+120?

Answer 1

use formula of n natural number sum

n ( n + 1 )/2

120 × 121
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2

= 60 × 121

= 7260

Answer 2

The sum of first n consecutive natural numbers is (n(n + 1))/2.

Here, n = 120

$1 + 2 + 3 +......+ 120 \\ \\ = \frac{120 \times 121}{2} \\ \\ = 60 \times 121 = 7260$

∴ 7260 is the answer.