Questions in Quiz C1W2

Course Q&A Natural Language Processing NLP with Classification and Vector Spaces
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I have some questions about the quiz questions:
Q1: Assume that there are 2 happy people and 2 unhappy people in a room. Concretely, persons A and B are happy and persons B and C are unhappy. If you were to randomly pick a person from the room, what is the probability that the person is happy?

In this question, B is both happy and unhappy. So, there are 3 people to pick, among them A and B are happy. Wouldn’t the probability be 2/3? But there is no such answer. Or even if we consider B as unhappy, it would be 1/3, but this answer is not available either. Is the duplication of B a mistake in the question, or there is something I’m missing?

Q5: Suppose that in your dataset, 25% of the positive tweets contain the word ‘happy’. You also know that a total of 13% of the tweets in your dataset contain the word ‘happy’, and that 40% of the total number of tweets are positive. You observe the tweet: '‘happy to learn NLP’. What is the probability that this tweet is positive?

P(happy|pos) = 0.25, P(happy) = 0.13, P(pos) = 0.4. So, P(pos|happy) = 0.25*0.4/0.13=0.7692308. But this answer is graded as wrong answer. Did I understood it wrong, or it is just the numerical precision tolerance problem?

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Hi, @Jack_Changfan .

Yes, I think Q1 wording choice is strange :slight_smile: I guess person B is Schrödinger’s (aka quantum) person and we should interpret that there are actually 4 persons in the room. So in that quantum :slight_smile: room the probability of picking happy person is 2 / 4 = 1/2

Regarding Q5 you guessed correctly that it is just the rounding problem and the correct answer is 0.77.

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well that makes sense on Q5. At first I tried “77%” and it said it wasn’t a number then I tried .769 (as I was sure the grader would accept a value within some bounds) and it said it was wrong.

That question seriously needs to be updated to articulate the type of number of level of precision. I was starting to question whether I understood it in the first place.

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+1 on that. Took 5 tries to get to the point of giving up - just add “with 2 significant digits” or change the grader to accept anything between .769 and .77 …

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