Quant Question Of The Day: 270
Numbers
Sumit added the first n natural numbers. However, he added one of the numbers twice, by mistake, and obtained the sum as 640. Find the number that was added twice.
Let the mstake be x and the number of natural numbers added be n
the sum of first n natural numbers is Sn = n(n+1)/2
n(n+1)/2 + x = 640
n = 35 , Sn = 630, Hence , x = 10.
When n = 36 , Sn = 666
for n = 34 , Sn = 595 and x has to be 45, which is not possible.
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