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What is the fewest number of pairs you need to test to guarantee you can get the flashlight on?

+2 votes
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You have a flashlight that takes 2 working batteries. You have 8 batteries but only 4 of them work.

What is the fewest number of pairs you need to test to guarantee you can get the flashlight on?

posted Oct 7, 2014 by Sandeep Otari

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1 Answer

+1 vote

7
You must first divide the batteries in three groups: a group of two batteries and two groups of three batteries each. Now you have made sure that one of the group has two working batteries.

Now both the groups with three batteries can form three possible combinations and the group with two batteries has just one combination.

3 + 3 + 1 = 7.

answer Nov 11, 2014 by Vrije Mani Upadhyay



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