SOLUTION: Hi! So, I have a question on probability. The question is students in the class take two tests. 20% of the class passed both tests and 57% of the class passed the first test. W

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Question 435545: Hi!
So, I have a question on probability. The question is students in the class take two tests. 20% of the class passed both tests and 57% of the class passed the first test. What percentage of those who passed the first test also passed the second test?
Thank you for your help!
Found 2 solutions by stanbon, robertb:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
The question is students in the class take two tests. 20% of the class passed both tests and 57% of the class passed the first test. What percentage of those who passed the first test also passed the second test?
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Draw a Venn diagram with 2 intersecting circles.
Label one circle "1st test"
Label the other circle "2nd test"
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Put 20% in the intersection.
Put 57%-20% = 37% in the 1st cicle that is not part of
the intersection.
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What percentage of those who passed the first test also passed the second test?
20/57 = 0.35 = 35%
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Cheers,
Stan H.

Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
P(2nd | 1st) = P(1st AND 2nd)/P(1st) = 0.20/0.57 = 0.35, to two decimal place, or around 35%.