Question
Consider Guwahati (G) and Delhi (D) whose temperatures can be classified as high (), medium () and low (). Let denote the probability that Guwahati has high temperature. Similarly, and denotes the probability of Guwahati having medium and low temperatures respectively. Similarly, we use , and for Delhi.
The following table gives the conditional probabilities for Delhi’s temperature given Guwahati’s temperature.
| Guwahati \ Delhi | |||
|---|---|---|---|
| 0.40 | 0.48 | 0.12 | |
| 0.10 | 0.65 | 0.25 | |
| 0.01 | 0.50 | 0.49 |
Consider the first row in the table above. The first entry denotes that if Guwahati has high temperature () then the probability of Delhi also having a high temperature () is 0.40; i.e., . Similarly, the next two entries are and . Similarly for the other rows.
If it is known that , , and , then the probability (correct to two decimal places) that Guwahati has high temperature given that Delhi has high temperature is _______.
Official answer and solution
- Accepted answers
- 0.6 to 0.62
- From
- Official GATE 2018 answer key
Solution
Apply the Law of Total Probability to find and Bayes' Theorem to find .
Given priors:
Conditional probabilities for Delhi high temperature from table:
Calculate the total probability of Delhi having high temperature:
By Bayes' Theorem, the posterior probability is:
Rounded to two decimal places, the probability is 0.60.
0.60
The answer is the one in the official GATE answer key. The solution is this site's own explanation.
Source
- Paper
- GATE 2018 Computer Science and Information Technology (CS)
- Question
- 54 of 65, printed as CS Q.44
- Section
- Computer Science and Information Technology
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