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ds question

by dunkin77 » Tue Jun 12, 2007 6:25 am
A certain list contains serveral diff integers. Is the product of the different intergers in the list +ve?

1) the product of greatest and smallest of the integers in the list is +ve
2) there is even no of integers in the list




Hi,

I don't have OA...but I think it's A. Can anyone confirm the answer?
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by mschling52 » Tue Jun 12, 2007 11:32 am
I think it is C - both together.

From (1) we know that the integers are either all positive or all negative since the greatest and least among them are either both negative or both positive. Still, we don't know if the product of them is positive or negative. Consider the set

S = {-5,-3,-1}

This satisfies (1), but the product of all the members is -15. However,

S = {-5,-4,-3,-1}

also satisfies (1) and the product is 60.

(2) alone clearly does not tell us anything about the numbers in the list.

However, combining (1) and (2), we know that the list is either all positive or all negative AND the number of items in the list is even. If they are all positive, clearly the product of them all is positive. If they are all negative and we know that there is an even number of elements, then the product will be positive as well, since the product of an even number of negative integers will always be positive.
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by dunkin77 » Tue Jun 12, 2007 12:11 pm
I think you're right. all negative + odd number will fail...so we need 2) as well. so, it must be C) Thank you! :)
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