An instructor surveyed her 390 students to find out their class and number of ex

Question

An instructor surveyed her 390 students to find out their class and number of exams they have during the week after spring break this semester. The results of the poll are shown in the table. For each of the following, no notation is necessary-you only have to show how you calculated your answers. Give your final answers as fractions. If one student is selected at random from this class, what is the probability that he or she is a freshman and has one exam during the week after spring break? has at least two exams during the week after spring break? is an upperclassman (junior/senior) or has no exams during the week after spring break?

Explanation / Answer

a)
Freshman and has one exam
This accounts for a total of 98 out of 390
So, 98 / 390, which is 49/195 ---> ANSWER

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b)
Atleast 2 exams :
Atleast 2 exams can mean exactly 2 or exatcly 3 exams
So, this makes up a total of 64 + 39, i.e 103 out of 390
So, 103 / 390 ----> ANSWER

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c)
Upperclassman or has no exams :
P(Upperclassman) + P(no exams) - P(uclassman and no exams)
No of upperclassmen = 77+52 = 129
No of people with no exams = 59
No of upperclassmen with no exams = 10+14 = 24

So, total = 129 + 59 - 24 = 164

So probability = 164/390 or 82 / 195 ----> ANSWER

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