Question

find the value of 1+2+3...+210

Answer 1

there are 210 terms
S210=210/2([2(1)+(210-1)1]
=105*211
=22155

Answer 2

You can claculate the sums of natural no.s by this equation .....
(n)(n+1)/2
Where n = the last no. In the series **
So , putting values,
(210)(210+1)/2= (210)(211)/2
= 22155
Done.

** This question can also be framed as
The sum of first n natural no.s ......(here it is , the sum of first 210 natural no.s )
So, n is that value