Question each-r
Each rock in a collection of rocks was classified as either igneous, metamorphic, or sedimentary, as shown in the frequency table.
| Classifiion | Frequency |
|---|---|
| igneous | |
| metamorphic | |
| sedimentary |
If one of these rocks is selected at random, what is the probability of selecting a rock that is igneous?
Each rock in a collection of 70 rocks was classified as either igneous, metamorphic, or sedimentary,
Medium-difficulty · SAT Math · Probability & Conditional Probability — Simple probability. Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.
Answer explanation
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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