## Problem Of The Week 39

**A set of 2009 numbers from (1-2009) is written on the board. You are allowed to replace any two of these numbers by a new number which is either the sum or the absolute difference of these numbers, after 2008 such operations, Which of the following cannot be the last number left on the board?**

**A) 1 B) 3 C) 4 D) 5) E) Cannot be determined **

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Option C 4

As the last number left would be odd coz whether a and b are replaced by a+b or a-b choosing both odd , both even or one odd and one even , no. of odds is always odd.

tyroOctober 2, 2008 at 12:23 pm

nice tyro!!

Good going !

outtimedOctober 2, 2008 at 12:29 pm