Question

Find the sum of first 30 natural no.s ORALLY

Answer 1

it is found by sum of n terms in AP

a=1
l=30

n=30

s=n/2(a+l)
s=15*31
s=465

how can it be done orally

Answer 2

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+
30=465