After astronaut Mark got to the dig, he collected rock specimens to take back to the Earth scientists. He packed the rocks into three sacks: one for igneous rocks, one for sedimentary and one for metamorphic. But, rushing to return to the aircraft before his portable oxygen ran out, he mislabeled all the sacks. How many rocks did he have to take out of how many sacks in order to find out what was in each one?
Answer:
One rock from one sack. If he were to open the sack labeled "igneous," for instance, and the rock turned out to be sedimentary, then he would know that the other two sacks could not contain sedimentary rocks. The other sacks then would have either igneous or metamorphic rocks in them. Since all the sacks were mislabeled, the one labeled "sedimentary" must then contain metamorphic and the one labeled "metamorphic" must contain igneous rocks.
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