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?  Choose the correct choice from the following options:
A) 5
B) 8
C) 7
D) 6
E) 4

Rationale: if you break the batteries into 3 groups : two groups of 3 and one group of 2 . by doing this you guarantee that one of the groups has 2 working batteries . both of the groups of 3 have 3 possible combinations of 2 batteries and the group of 2 only has 1 combination . so , 3 + 3 + 1 = 7 tries at most to find two working batteries .
Answer: C