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Quantitative Aptitude

Sum of Consecutive Numbers

The integers ...

Question

The integers 1,2,….. 40 are written on a blackboard. The following operation is then repeated 39 times; in each repetition, any two numbers, say a and b, currently on the blackboard, are erased and a new number a+b-1 is written. What is the number left on the board at the end?

A

820

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B

821

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C

781

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D

819

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E

780

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Solution

The correct option is C 781
Option (C) is the correct answer. Check the video for the approach.

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