[Brain teaser] 6.1 Bottles of Pills

Question

You have 20 bottles of pills. 19 bottles have 1.0 gram pills, but one has pills of weight 1.1 grams.

Given a scale, how to find the heavy bottle only scaling ONCE?

Solution

Take 1 pill from Bottle 1, 2 pills from Bottle 2, and so on. We’ll expect (1 + 2 + … + 20) = 210 gram of pills.

The answer would be {(weight - 210 grams) / 0.1}.