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: Two men, Watson and Holmes, are out in the extremely dry forest. They are completely surrounded by a large forest fire on one side and a dangerous cliff on the other. The wind is blowing the forest fire towards them and the cliff. The fire will reach them in about one day.
Holmes turns to Watson, "I have matches, berries, and enough water for a day. We aren't going to die." How can they avoid getting swallowed up by the forest fire?
Answer: They can start a fire of their own with the matches and the wind will blow that fire in the same direction as the forest fire and they can take refuge in the section of the forest they burn down.