Question

what is the approximate square root of the sum of first 20 natural numbers

Answer 1

natural numbers are in AP
a = 1, d = 1, n = 20
Sn = (2a + (n-1)d)n/2
S20 = (2 + 19)10 = 210
√210 = 14.49 (approx)

Answer 2

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20=>210

$\sqrt{210} = 14.491$

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