# You have a flashlight and 8 batteries

Question: 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?

Riddle Discussion

By: 0wewewe0 on 13/9/14

7. Let's name batteries ABCDEFGH. First let's test AB, CD, EF, GH (4 tests). in worst possible case neither on those pairs will work but we now know for sure that each pair has at least one working battery. Now we take AB and CD and try different combinations of them : AC, BC, AD, BD. In worst possible case the first three(3 tests) dont work and now we know for sure that the forth must work.

### Similar Riddles

##### Cheetah and a Burger (medium)

By Dean

Question: What do you get when you cross a cheetah and a burger?

##### Tastes better than it smells (medium)

Question: What tastes better than it smells?

##### Goes in the water black and comes out red (medium)

Question: What goes in the water black and comes out red?

##### What loses its head in the morning (easy)

Question: What loses its head in the morning and gets it back at night?

##### Riddle #997 (easy)

Question: What two things can you never eat for breakfast?