2008-01-07

Pills

Here's a puzzle that my friend Kevin sent me.*

You have five jars of pills. All the pills in one jar only are contaminated. The only way to tell which pills are contaminated is by weight. "Good" pills weigh 10 grams while "bad" (contaminated) ones weigh 9 grams. You are given a scale and can make just one measurement with it. How can you tell which jar holds the contaminated pills?

Here's the answer to a follow-up question I had; it may help you:

Q: Is the scale a balance scale?
A: No; it's a regular kitchen scale that tells you how many grams something weighs.

* Kudos to Mark for solving this in about 30 seconds.

4 comments:

Mark Hanington said...

Beginner's luck.

Molly said...

You take 4 pills from one bottle, 3 pills from another, 2 pills from another, and 1 pill from another. If the total weight is 100 grams you know the bottle that you didn't take any pills from is the bad one, if TW=99 grams, [left as an exercise for the reader]

fiona-h said...

oh Molly! You are SO SMART :-)

Darren said...

Ah yes... didn't think about actually *opening* the jars.