Question

find the sum 1+2+3+...+20​

Answer 1

The given series is that of natural numbers. Hence, we can find the sum using the relation.

S

n

=

2

n(n+1)

here, n = 20

S

20

=

2

20(20+1)

=

2

20×21

S

20

=210

Answer 2

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