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The data in the table show cell phone ownership status by grade level

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Bunuel
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The data in the table show cell phone ownership status by grade level [#permalink] New post   23 Mar 2018, 00:00
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The data in the table show cell phone ownership status by grade level of 300 middle school students. If one of the 300 students is randomly selected, what is the probability that the student owns a cell phone, given that the student is a seventh grader?




A. 11/60

B. 11/100

C. 163/300

D. 55/163

E. 11/20


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Hatakekakashi
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Re: The data in the table show cell phone ownership status by grade level [#permalink] New post   23 Mar 2018, 00:17
Bunuel wrote:
The data in the table show cell phone ownership status by grade level of 300 middle school students. If one of the 300 students is randomly selected, what is the probability that the student owns a cell phone, given that the student is a seventh grader?




A. 11/60

B. 11/100

C. 163/300

D. 55/163

E. 11/20


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2018-03-23_1057.png



total students 300

7th grader with cellphone 55

prob = 55/300 = 11/60
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hoang221
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Re: The data in the table show cell phone ownership status by grade level [#permalink] New post   23 Mar 2018, 10:21
Bunuel wrote:
The data in the table show cell phone ownership status by grade level of 300 middle school students. If one of the 300 students is randomly selected, what is the probability that the student owns a cell phone, given that the student is a seventh grader?




A. 11/60

B. 11/100

C. 163/300

D. 55/163

E. 11/20


Show Spoiler
Attachment:
2018-03-23_1057.png


The probability that the random selected student will be a 7th grader and own a cell phone will be: \(\frac{55}{300} = \frac{11}{60}\) (A)
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Chakolate
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Re: The data in the table show cell phone ownership status by grade level [#permalink] New post   23 Mar 2018, 13:15
Bunuel wrote:
The data in the table show cell phone ownership status by grade level of 300 middle school students. If one of the 300 students is randomly selected, what is the probability that the student owns a cell phone, given that the student is a seventh grader?




A. 11/60

B. 11/100

C. 163/300

D. 55/163

E. 11/20



The question says "GIVEN that the student is in the 7th grade". That means we can ignore the rest of the chart and only look at the 7th grade row. 55/100 is 11/20, answer E.
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hoang221
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Re: The data in the table show cell phone ownership status by grade level [#permalink] New post   23 Mar 2018, 14:09
Chakolate wrote:
Bunuel wrote:
The data in the table show cell phone ownership status by grade level of 300 middle school students. If one of the 300 students is randomly selected, what is the probability that the student owns a cell phone, given that the student is a seventh grader?




A. 11/60

B. 11/100

C. 163/300

D. 55/163

E. 11/20



The question says "GIVEN that the student is in the 7th grade". That means we can ignore the rest of the chart and only look at the 7th grade row. 55/100 is 11/20, answer E.


We're asked to choose 1 student from the total of 300, so your answer is wrong!
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Chakolate
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Re: The data in the table show cell phone ownership status by grade level [#permalink] New post   23 Mar 2018, 19:23
hoang221 wrote:

We're asked to choose 1 student from the total of 300, so your answer is wrong!


You say I'm wrong, I say you're wrong. I guess we'll have to wait until Bunuel weighs in.
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leonardich
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The data in the table show cell phone ownership status by grade level [#permalink] New post   07 Jul 2019, 08:38
Use Bayes' theorem. P(A|B) = P(B|A)P(A)/P(B). We have:

P(A|B) is the prob that given a student in 7th grade, he/she has a smartphone (what we want to find).

P(B|A) is the prob. that given a student in 7th grade with a smartphone, he/she is in the 7th grade. Therefore, P(B|A) = 1.

P(A) is the prob. that a 7th grade student has a smartphone. Hence, P(A) = 55/300.

P(B) is the prob. that a student is in 7th grade. Thus, P(B) = 1/3.

Finally, P(A|B) = 1(55/300)/3 = 165/300 = 11/20.

Hope this helps.
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The data in the table show cell phone ownership status by grade level [#permalink]
07 Jul 2019, 08:38
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