My remote control needs two new batteries, but when I went to get replacements I found that the four good batteries got mixed in with four bad batteries. The only means of determining if the batteries are good is to put two into the remote and see if it works. The remote works with two good batteries and is unresponsive if I have at least one bad battery in it.

What is the minimum number of tries I need to guarantee that I get two good batteries?

Try batteries 1 and 2

then 3 and 4

then 5 and 6

then 7 and 8.

If any of these pairs work, use that pair and stop.

If none of the pairs works, each has one good and one bad battery. So try 1 & 3. If that doesn't work, one or both are bad. Try 1 and 4. If that doesn't work try 2 and 4. Finally if none of those work, 2 and 3 must be a good pair.

That was 8 tries in all in the worst-case scenario.

Posted by Charlie on 2013-11-11 17:27:25