Question: You work at a factory that produces dumbbell weights for lifting. One of the 10 machines has been producing weights that are always 1 pound less than the rest of the machines. You have a large scale used to weigh the weights for quality control. How could you find the defective machine by using the scale only once? You are allowed to make as many weights with the machines as you please.
Answer: From each machine you make a different number of weights and however many pounds the scale is off from what it should be corresponds to the machine that made that many weights.
From machine 1 you make 1 weight, machine 2 you make 2 weights...
If the machine is off by 1 pound you know it was machine 1 that was off.
Question: A rich man suddenly dies from a cut on his finger. The next day, two men appeared and claimed to be his long-lost son. They both fit the description in the will and had all the necessary documents. The family attorney proposed a blood test. One man agreed while the other point blank refused. The one who agreed was arrested for fraud at once. The second man was accepted as the heir. Why?
Answer: He was a hemophiliac, like his father, who died from a small cut. The blood test would kill him.