Question

1+2+3+4+5+............+20 find the value without adding

Answer 1

use
Sn= n(n+1)/2



20×(20+1)/2. u Will get your answer

Answer 2

s(n) = n(n+1)/2

= 20(20+1)2

= 20×21/2

= 420/2

= 210

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