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Probability and conditional probability SAT question

Math · Problem-Solving and Data Analysis · Easy · Answer it here, explanation included.

Each rock in a collection of rocks was classified as either igneous, metamorphic, or sedimentary, as shown in the frequency table.

Classification Frequency
igneous
metamorphic
sedimentary

If one of these rocks is selected at random, what is the probability of selecting a rock that is igneous?

ExplanationShow

Choice D is correct. If one of the rocks in the collection is selected at random, the probability of selecting a rock that is igneous is equal to the number of igneous rocks in the collection divided by the total number of rocks in the collection. According to the table, there are igneous rocks in the collection, and it's given that there's a total of rocks in the collection. Therefore, if one of the rocks in the collection is selected at random, the probability of selecting a rock that is igneous is .

Choice A is incorrect. This is the number of igneous rocks in the collection divided by the number of sedimentary rocks in the collection, not divided by the total number of rocks in the collection.

Choice B is incorrect. This is the number of igneous rocks in the collection divided by the number of metamorphic rocks in the collection, not divided by the total number of rocks in the collection.

Choice C is incorrect. This is the number of igneous rocks in the collection divided by the number of rocks in the collection that aren't igneous, not divided by the total number of rocks in the collection.

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