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Interview Question for Sales and Trading at UBS:
Feb 11, 2010

What is the sum of 1-40?

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Answers & Comments (5)

Feb 11, 2010

by Interview Candidate:

820
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2 of 2 people found this helpful

Mar 21, 2010

by blue:

We can have the sum by using the following formula
N * (N + 1) / 2

So we have:
40 * (40 + 1) / 2 = 820
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0 of 3 people found this helpful

Dec 30, 2010

by Evandro:

Since he isn't asking to sum all the numbers from 1 to 40:

sum of 1 and 40 = 41
OR
sum of 1 + -40 = -39
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3 of 3 people found this helpful

Jan 11, 2011

by scienceguy:

Any sum like this is easy. take the lowest and highest... 1 +40 = 41, then the next highest and the next lowest. 2 + 39 = 41. Realize that there are 20 such pairs. 20 * 41 = 820.
For the numbers 1 - 100, 1 + 100 = 101, 2 + 99 = 101; there are 50 such pairs, so 50 * 101 = 5050
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Jun 13, 2011

by an87:

http://brainteaserbible.com/interview-brainteaser-sum-of-the-numbers-from-1-to-50
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