Answer: 0.25
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Explanation:
We randomly selected an 8th grader. This means we know 100% that the person is in 8th grade and we do not consider the first row of 7th graders. We only focus on row 2.
In row 2, we have 0.11 as the probability of an 8th grader taking the bus (see note below) and 0.44 is the probability of selecting an 8th grader. So 0.11/0.44 = 0.25 is our answer.
You can multiply each value in the table by 100. The 0.11 will become 11 and the 0.44 will turn into 44. This tells us that out of 100 students (7th & 8th graders), 44 are in 8th grade and 11 are 8th graders who take the bus. Focusing solely on those 44 eighth graders, we find that the probability of picking someone who takes the bus is 11/44 = 0.25, which is the same answer as before.
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note: if we did not know the person selected was an 8th grader, then the answer to "what is the probability an 8th grader takes the bus" would be 0.11; however we do have prior knowledge the person selected is in 8th grade.
