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How to add 1+2+3+4+....+100

Akhilesh Choudhary

09/03/2017 1 0

Simple trick

Let X=1+2+3+...+100

Now add same series in reverse order as

100+99+98+........+1 = X

Now 2X = 101+101+101+101+......100times

So 2X= 101*100

2X= 10100

X=5050

This formula comes like this = n(n+1)/2 where n is the last number of the series

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