# Tagged Questions

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### Average number of people required to find a pair with same birthday

I have to find the expected number of people required to find a pair with same birthday. This is what I tried: Assume that there are $M$ possible birthdays, then following the definition for expected ...
283 views

### 3 trams are coming every 10, 15 and 15 minutes. On average, how long do I have to wait for any tram to come?

3 trams are coming to the stop every 10, 15 and 15 minutes. On average, how long do I have to wait for any tram to come? It's a practical problem, not some kind of a riddle for which I have a ...
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### Difference between $\sum_{i=1}^{k}{\frac{s_i}{kn_i}}$ and $\frac{\sum_{i=1}^{k}{s_i}}{\sum_{i=1}^{k}{n_i}}$

I am getting confused at how to calculate the average probability. Suppose we repeat a kind of binary survey $k$ times each of which was done on a completely separate sample group. For each $i^{th}$ ...
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### Normal Distribution with Regards to Time and Percentages

The length of time for students to complete a test is found to be normally distributed with mean 70 minutes and standard deviation 12 minutes. How long should the time for the test be if we wish for ...
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### The Exponential decay.

i am studying semiconductor physics. there is a paragraph about Drude model in E.spenke's book "Electronic semiconductors" page 259 in art §9: "if on the average, a time $τ$ elapses between two ...
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### Minimum sample size to obtain population mean?

Knowing the average of a population, how could I evaluate an expected sample average based on k_sample? Data Info: Variance and standard deviation: $\sigma^2= 0.18500975256337462$ ...
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### Mean/ Expected Value of $X^4$

$\def\Var{\mathop{\rm Var}}$Can anyone help me prove that Expected Value of $X^4$ is $3\Var(X)^4$, if the Expected Value of $X$ is zero and $\Var(X)$ is the Variance of $X$? Thanks!
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### Game of bullets

Lets say with have a game with 10 targets. In each turn the participant shoots X number of different and random targets, where X is a random whole number between 0 and 10 (included). Game ends when ...
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### Geometric Mean of an Interval

Is there any way to calculate one? If it't not clear what I mean, here's an example: Starting with an initial value, keep multiplying it by some random amount on the interval [1, 2] at regular ...
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### Probability question help

A company that sells annuities must base the annual payout on the distribution of the length of life of the participants in the plan. Suppose the distribution of male participants' lifetimes is ...
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### Difference between $\frac{1}{n} \sum_{i=0}^n \frac{b_i}{a_i+b_i}$ and $\frac{\sum_{i=0}^n b_i}{\sum_{i=0}^n a_i + b_i}$

Consider scenario like this: each user can add movies. each user can rate movies he added. I want to know how many movies average user has unrated (as in average percentage). Let's translate this ...
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### About a special way to find the average waiting time to get a sequence

A friend of mine taught me the following question: You have a coin. When you toss it up, heads you note $1$, tails you note $0$. Then, tossing it up repeatedly, let's find the average waiting time to ...
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### Expected average of number of tiles empty

I have a grid of 3x4 and every tile on the grid has a corresponding chance of being empty. This chance is given. For example, consider the following grid:  \frac{14}{15} \frac{1}{3} \frac{8}{13} ...
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### change in sampling results and sample size

I am working on a problem, I have an experiment that each sampling gives me a numerical result. I want to create once a baseline of results that will give me very meaningful results. after creating ...
327 views

### Puzzle in Percentages

Okay, this is a real-time problem. The following is a picture of Customer satisfaction rating, which was displayed next to an item in an online shopping website. Satisfied customers click the ...
81 views

### Most Probable Average Marks

There is a class of 40 students. A professor conducted a quiz on which consisted of 10 Multiple Choice Questions. Each question had 4 options, out of which only one is correct. Each question carried 1 ...
24 views

### Inference the time a process would take depending on the number of threads

I have several datasets consisting on: Number of threads n Start process time t1 Stop process time ...
63 views

### Calculating expected value

Here is the problem. In a game(shown below) with the marker in the center on each turn the marker moves to a neighbouring region with all positions equally likely and the player collects the cash ...
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### Probability cut-off

Is there a probability cut-off point? e.g. if the probability of something keeps halving do you stop at a certain point and say the rest of the possibilities are negligible? What do you do then? ...
223 views

### Definition of random

Suppose that you has to guess given a set of numbers If they are random. The mathematical expectation Is there a definition of randomness that allow this prove/test? Is even possible? if so: How ...
218 views

### math distribution of averages and distribution of standard deviation for comparison of bytes

Let me change my question: I have a sequence of 512 numbers (these 512 numbers can have a value between 0 and 255) (in computer mode these numbers can be between 00000000 and 11111111 (bits)). For ...
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### Probability value in a skewed data

A question goes like this: Given that there 2 questions out of 3 questions to pass an exam and follow are details of number of people who attended the questions correctly, what is the maximum number ...