The Mystery of the Heavier Ball
You have eight identical balls, but one is slightly heavier than the rest. The other seven weigh exactly the same. You also have a balance scale, but you’re only allowed to use it twice.
How can you figure out which ball is the heavier one?
Show Answer
Answer:
Divide the balls into three groups:
Group 1: Three balls
Group 2: Three balls
Group 3: Two balls
First weighing: Place Group 1 on one side of the scale and Group 2 on the other.
If the scale balances, the heavier ball is in Group 3 (the two balls that weren’t weighed). You can then weigh these two against each other to find the heavier one.
If the scale tips, you now know the heavier ball is in the group that weighed more.
Second weighing: Take the three balls from the heavier group and weigh two of them against each other.
If the scale balances, the heavier ball is the one you didn’t weigh.
If the scale tips, the heavier ball is the one that made the scale go down.
This method guarantees that you’ll find the heavier ball in just two weighings!