# Tagged Questions

This tag is for basic questions about probability and for questions in which one wants to calculate a probability, expected value, variance, standard deviation, or similar quantity. For questions about the theoretical footing of probability (especially using measure theory), please ask under (...

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### AMC12B Problem, probability

An unfair coin lands on heads with a probability of $\tfrac{1}{4}$. When tossed $n$ times, the probability of exactly two heads is the same as the probability of exactly three heads. What is the value ...
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### 3 urns, each with 4 balls. select one ball from each

Three urns are labeled $1,2,3$. Each urn contains $4$ balls labeled $1,2,3,4$. A ball is drawn from each urn such that any ball is equally likely to be drawn. The number on the ball is compared to the ...
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### 4 Sided dice - flawed logic?

If we had a 4 sided dice (numbers 1,2,3,4 on the faces) and rolled it 6 times and recorded the results. What would be the probability that we rolled the same number 3 or more times? (Such as rolling ...
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### Probability with flipping a coin 6 times

I have a fair coin and I flip it 6 times, here are the events: $Pr(A)$ = "the coin comes up heads at least 4 times" $Pr(B)$ = "the number of heads is equal to the number of tails" $Pr(C)$ = "there ...
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### Optimizing Choice of Life Partner

In this link, Hannah Fry mentions that a mathematical argument has been made towards the probabilistically optimal strategy for picking someone to settle down with. The claim is as follows: If we ...
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### Smallest n to align sample mean with population mean

There's a question in my book that I just do not understand. This is it in its entirety: Let $\bar{X}$ be the sample mean of a random sample of size $n$ from a normal distribution with a variance ...
### Expected number of coin tosses to obtain first tail when probability of heads is $p$
Suppose a coin is tossed independently and repeatedly with probability of heads equal to $p$. What is the probability of only heads in the first $n$ tosses? $Try:$ I think since $p$ is probability ...