# What is the least number of attempts to make the flashlight work?

25 views

You are camping at night and are about to go out for a walk.

You have a flashlight with no batteries in it.

You realize you are carrying 8 batteries out of which only 4 are charged batteries and the other 4 are uncharged.

The flashlight needs 2 charged batteries to work.

You do not know which batteries are charged and which ones are not.

What is the least number of attempts to make the flashlight work?

(An attempt consists of putting two batteries in the flashlight and checking if the flashlight works or not.)

posted Jun 14, 2018

Min 1, max 7 attempts

Least number is one- if you are lucky you can get it work
Maximum number is 7- you need to group batteries in 3/3/2, at least one group will have 2 working batteries. With group of 3 you have 2 attempts, with group of 2- only one so maximum number of attempts is 3+3+1=7

Similar Puzzles
+1 vote

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?

+1 vote
+1 vote

What is the least number of coins required to have an exact change for all possible items that cost from one cent up to and including one dollar in one-cent increments?