Suppose you have four people that need to cross a bridge in the night. The bridge can hold the weight of two people at the same time and each person takes 1,2,5,10 minutes. What's the minimum time that they need to cross the bridge?
Part A Weigh 3 balls against 3 other balls on the balancing scale (leaving the 3 remaining balls out). If one of the weighed sides is heavier than the other, keep the heavier side's 3 balls and remove the other 6 balls from the exercise. On the other hand, if neither of the weighed sides is heavier than the other, remove from the exercise the 6 weighed balls and keep the 3 un-weighed balls. If any balls that haven't been removed from the exercise are on the balancing scale, remove them from the balancing scale. Part B With the 3 balls kept, put one on each side of the balancing scale and keep the remaining 1 aside. If 1 of the 2 balls weighed in Part B is heavier, that's the ball you're trying to find. On the other hand. if both side weighs the same, the remaining 1 aside is the ball you're trying to find.
1. Double check it was a mistake, rather than something I did for a good reason that I had forgotten. 2. Report it to my manager/senior person on the client/compliance team, depending on company policy.