In the heavier ball puzzle, which initial action is the correct first weighing?

• A. Weigh three balls against three balls.
• B. Divide the balls into three groups of three and weigh two groups against each other.
• C. Weigh all nine balls at once.
• D. Weigh a single ball against another ball.

Answer: (B)

Maximize the information you get from the first weighing. A balance scale has three possible outcomes, so the best move is to split the nine balls into three equal groups of three and weigh two of them against each other. If one side is heavier, the heavier ball is in that trio; if they balance, the heavier ball is in the third trio. Either way, you’re left with exactly three candidate balls for the next weighing, which lets you identify the heavier ball with one more weighing. Weighing fewer balls first or trying to weigh all nine isn’t as informative, and comparing one ball against another isn’t efficient for narrowing down nine possibilities. This initial three-on-three approach sets up a definitive solution in the fewest steps.