You are given eight coins and told that one of them is counterfeit. The counterfeit one is slightly heavier than the other seven. Otherwise, the coins look identical. Using a simple balance scale, how can you determine which coin is counterfeit using the scale only twice?
First weigh three coins against three others. If the weights are equal, weigh the remaining two against each other. The heavier one is the counterfeit. If one of the groups of three is heavier, weigh two of those coins against each other. If one is heavier, it’s the counterfeit. If they’re equal weight, the third coin is the counterfeit.
If a piece of rope was tightly wrapped around the earth and you added 3 feet to its length, how high could you uniformly raise it from the earth’s surface?
What must be in the oven yet can not be baked? Grows in the heat yet shuns the light of day? What sinks in water but rises with air? Looks like skin but is fine as hair?