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 d1 or more ? (Posted on 2016-03-07)
A problem from the 2004 Harvard-MIT Math Tournament:

Zach chooses five numbers from the set {1, 2, 3, 4, 5, 6, 7} and tells their product to Claudia. She finds that this is not enough information to tell whether the sum of Zachâ€™s numbers is even or odd. What is the product that Zach tells Claudia?

I believe it is a d1 puzzle.

Are you on my side?

 See The Solution Submitted by Ady TZIDON No Rating

Comments: ( Back to comment list | You must be logged in to post comments.)
 re: Why I'm with Ady Comment 4 of 4 |

The process described by Jer is exactly what I have experienced.

I believe it took me less than 20 seconds:

Anyone used to fiddle with numbers( including myself) knows that 2*6 and 4*3 are the only sample within the nine non-zero digits of of two distinct couples (a,b) & (c,d) that produce   the same result when multiplied, and in the same time  the sums have opposite parities.

Thus it boils down to mentally evaluate 1*5*7*12=60*7=420.

I estimate that I've spent over 5 min. trying to justify myself by typing the above..

But, to quote Jer, it was a TOURNAMENT (sic!) question!

 Posted by Ady TZIDON on 2016-03-07 12:08:41

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