7k views

### On average, how many friends would I need to have to have at least one friend's birthday every day? [duplicate]

I know that because of the birthday problem, even after 365 friends, you're going to have a lot of doubles and that there's also an infinitesimal chance that even with infinite friends that there's ...
600 views

### How many throws of a die until every possible result is obtained? [duplicate]

A die is thrown until every possible result (i.e., every integer from 1 to 6) is obtained. Find the expected value of the number of throws. How do I do that? I understand that probability for the ...
7k views

### How do you calculate probability of rolling all faces of a die after n number of rolls? [duplicate]

Possible Duplicate: Expected time to roll all 1 through 6 on a die Probability of picking all elements in a set Im pretty new to the stackexchange, and posted this is statistics, and then ...
1k views

### How many random samples needed to pick all elements of set? [duplicate]

If repeatedly picking a random element from a set, what is the expected number of times I'd have to pick before seeing all the elements of the set? Edit: when picking an element, it is simply counted ...
2k views

### How many papers do you expect to hand in before you receive each possible grade at least once? [duplicate]

A particular professor is known for his arbitrary grading policies. Each paper receives a grade from the set {A, A-, B+, B, B-, C+}, with equal probability, independently of other papers. How many ...
2k views

### How do wer find this expected value? [duplicate]

I'm just a little confused on this. I'm pretty sure that I need to use indicators for this but I'm not sure how I find the probability. The question goes like this: A company puts five different ...
2k views

### throwing a dice repeatedly so that each side appear once. [duplicate]

Pratt is given a fair die. He repeatedly throw the die until he get at least each number (1 to 6). Define the random variable $X$ to be the total number of trials that pratt throws the die. or ...
1k views

### Coupon Collector's Problem with X amount of coupons already collected. [duplicate]

I am having an issue with understanding how to calculate a specific case of the Coupon Collector's Problem. Say I have a set of 198 coupons. I learned how to find the estimated amount of draws to see ...
808 views

### Expected number of rolls to get all 6 numbers of a die [duplicate]

I've been thinking about this for a while but don't know how to go about obtaining the answer. Find the expectation of the times of rolls if u want to get all 6 numbers when rolling a 6 sided die. ...
179 views

### Expected value from popping bubbles [duplicate]

This is a fairly simple math problem from a programming challenge but I'm having trouble wrapping my head around it. What follows is a paraphrase of the problem: ...
316 views

### How many times must you roll a die until each side has appeared? [duplicate]

Let $X$ be the random variable which denotes the number of times a die has been rolled till each side has appeared. The order does not matter. We are trying to find $E[X]$. Let $X_i$ be a random ...
390 views

### How many iterations does it take to cover a range with random values? [duplicate]

Let's say I have a random number generator that generates integers uniformly from 0 to n-1 (where n is some positive integer). What is the expected number of iterations after which all the values 0..n-...
467 views

### calculating expected number of packets. [duplicate]

To go with the Lego Movie, Lego sell minifigures of the characters from the movie. They are sold in packets, where each packet contains one minifigure, and from the outside of the packet it is ...