MHB Practice test help - probability from data

AI Thread Summary
The discussion focuses on calculating probabilities related to orthopedic surgeries involving knee problems. The first question's answer is confirmed as 26%, while the second question's answer is clarified to be approximately 18%, not 2%. To find the probabilities for questions 2 and beyond, the formula involves dividing the number of occurrences of the event by the total number of occurrences within the relevant category. Participants are encouraged to apply this method to questions 3 and 4 as well. Accurate understanding of these calculations is essential for solving the practice test effectively.
CosmoK123456
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Having some trouble with this. I think the answer to question 1 is 26% and question 2 is 2%. I'm not sure when to divide by 163 or 100??
practice test help:
About 26% of orthopedic surgeries involves knee problems. The following table summarizes data collected from a sample of adults who have knee surgery. (Source: American Academy of Orthopedic Surgeons)

age, full knee replacement, no knee replacement
18-44,2, 9
45-64,25, 11
65-74,43,27
75-84, 27, 14
85-older,3, 2 1) What is the probability that an orthopedic surgical case selected at random involves
knee surgery?

2) What is the probability that a person from ages 18 – 44 who has knee surgery has a
full knee replacement?

3) What is the probability that a person from 45 – 64 who has knee surgery has a full
knee replacement?

4) What is the probability that a person who has knee surgery has a full knee
replacement?
 
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Welcome to MHB, CosmoK! :)

CosmoK123456 said:
Having some trouble with this. I think the answer to question 1 is 26% and question 2 is 2%. I'm not sure when to divide by 163 or 100??
practice test help:
About 26% of orthopedic surgeries involves knee problems. The following table summarizes data collected from a sample of adults who have knee surgery. (Source: American Academy of Orthopedic Surgeons)


[TD="align: center"]age[/TD]
[TD="align: center"]full knee replacement[/TD]
[TD="align: center"]no knee replacement[/TD]

[TD="align: center"]18-44[/TD]
[TD="align: center"]2[/TD]
[TD="align: center"]9[/TD]

[TD="align: center"]45-64[/TD]
[TD="align: center"]25[/TD]
[TD="align: center"]11[/TD]

[TD="align: center"]65-74[/TD]
[TD="align: center"]43[/TD]
[TD="align: center"]27[/TD]

[TD="align: center"]75-84[/TD]
[TD="align: center"]27[/TD]
[TD="align: center"]14[/TD]

[TD="align: center"]85-older[/TD]
[TD="align: center"]3[/TD]
[TD="align: center"]2[/TD]

1) What is the probability that an orthopedic surgical case selected at random involves
knee surgery?

2) What is the probability that a person from ages 18 – 44 who has knee surgery has a
full knee replacement?

3) What is the probability that a person from 45 – 64 who has knee surgery has a full
knee replacement?

4) What is the probability that a person who has knee surgery has a full knee
replacement?

You have question 1 correct.

For question 2 and following, you need to know that the probability that something occurs, is the number of occurrences divided by the total number of occurrences.
In a formula:
$$\text{probability on event} = \frac{\text{number of occurrences of event}}{\text{total number of occurrences}}$$
The catch is that in your case the total number is the total number within a certain category.

Applied to question 2, you have:
\begin{aligned}
P &= \frac{\text{number of persons from ages 18 – 44 who have knee surgery who also have a
full knee replacement}}{\text{total number of persons from ages 18 – 44 who have knee surgery}} \\
&= \frac{2}{2 + 9} \\
&= \frac{2}{11} \\
&\approx 18\%
\end{aligned}

Perhaps you can apply it to questions 3 and 4?

EDIT: Fixed to 18% as Prove It remarked.
 
Last edited:
I like Serena said:
Welcome to MHB, CosmoK! :)
You have question 1 correct.

For question 2 and following, you need to know that the probability that something occurs, is the number of occurrences divided by the total number of occurrences.
In a formula:
$$\text{probability on event} = \frac{\text{number of occurrences of event}}{\text{total number of occurrences}}$$
The catch is that in your case the total number is the total number within a certain category.

Applied to question 2, you have:
\begin{aligned}
P &= \frac{\text{number of persons from ages 18 – 44 who have knee surgery who also have a
full knee replacement}}{\text{total number of persons from ages 18 – 44 who have knee surgery}} \\
&= \frac{2}{2 + 9} \\
&= \frac{2}{11} \\
&\approx 22\%
\end{aligned}

Perhaps you can apply it to questions 3 and 4?

\displaystyle \frac{2}{11} \approx 18\%, not 22%...
 
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