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What is the sum 1+2+3,....+40.How do you calculate quickly?

 How to calculate the sum easily and quickly?

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+31+32+33+34+35+36+37+38+39+40

 

What is the sum?

Look for the easiest way to calculate the sum.

The numbers 1,2,3,4,......,40  is an AP sequence

See the way below.

 

 

AP 

First term 1 

last term 40

d=1 and n=40

S= (a1+an)*n/2

(1+40)*40/2=

41*20=820

 

 

 

 

 

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