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A routine exercise designed to test one's knowledge; often from a textbook, course, or test used for a class or self-study. This community's policy is to "provide helpful hints" for such questions rather than complete answers.

31 votes
4 answers
2k views

Is the result of an exam a binomial?

Is X binomial distributed? The professor's answer was: Yes, because there is only right or wrong answers. My answer: No, because each question has a different "success-probability" p. … As I did understand a binomial distribution is just a series of Bernoulli-experiments, which each have a simple outcome (success or failure) with a given success-probability p (and all are "identical" …
Paul's user avatar
  • 445
27 votes
Accepted

Will the fact that my Italian son is going to attend a primary school change the expected nu...

B is the binomial distribution. … Note that starting with $E(X|X\geq1)$ does not give the proper answer, as knowing that a specific child is Italian violates the exchangeability assumed by the binomial distribution. …
Erik's user avatar
  • 7,309
26 votes
Accepted

Is the result of an exam a binomial?

Your professors answer assumes that all questions have same probability of "success" and are independent, since binomial is a distribution of a sum of $n$ i.i.d. Bernoulli trials. … The distribution could be approximated with binomial, or Poisson, but that's all. Otherwise you're making the i.i.d. assumption. …
Tim's user avatar
  • 141k
25 votes

What is the expected number of children until having the same number of girls and boys?

There are $Binomial[2n,n]/(2n-1)$ ways for the couple to achieve parity for the first time with $n$ boys and $n$ girls. These are twice the Catalan numbers. … So the expected value would be $$\sum \frac{Binomial[2n,n]}{(2n-1)2^{2n}}2n $$ but the sum is divergent: the expected number of children is infinite. …
user avatar
22 votes
Accepted

What must someone know in statistics and machine learning?

There are a few crucial distributions everyone must know: Normal, Binomial, Beta, Chi-Squared, F, Student's t, Multivariate Normal. …
22 votes
Accepted

How does the beta prior affect the posterior under a binomial likelihood

To answer your first question we just need to use Bayes' Theorem to update our binomial likelihood with the beta prior. … Now, let $x_i\sim\text{Binomial}(N_i,\theta)$ and $\theta\sim\text{Beta}(\alpha,\beta)$. …
user avatar
21 votes

How to assess whether a coin tossed 900 times and comes up heads 490 times is biased?

Then the number of heads has *binomial distribution with mean $(900)(1/2)=450$, and standard deviation $\sqrt{(900)(1/2)(1/2)}=15$. … In the normal approximation to the binomial, we get a better approximation to the probability that the binomial is $\ge 490$ by calculating the probability that the normal is $\ge 489.5$. …
user avatar
21 votes

Risk of extinction of Schrödinger's cats

It's unclear what "risk of extinction category" means, but it appears the question asks to compute the distribution of the sum of 15 independent binomial variates having the given expectations. …
whuber's user avatar
  • 334k
16 votes
Accepted

Unbiased estimator of variance of binomial variable

. $$ As you see we do not need the hypothesis that the variables have a binomial distribution (except implicitly in the fact that the variance exists) in order to derive this estimator. …
gui11aume's user avatar
  • 14.9k
15 votes

How to choose the null and alternative hypothesis?

.$$ This is a one-sided binomial proportion test. $H_a$ is the statement that, if it were true, would need to be strongly supported by the data we collected. …
heropup's user avatar
  • 5,521
14 votes
Accepted

Probability of each of the three Christmas puddings having exactly 2 coins

$Pr(A=2)$ is a simple binomial calculation: $A\sim Binom(6, 1/3)$, so $Pr(A=2) = {6\choose 2}(1/3)^2(2/3)^4 = 80/243$. …
josliber's user avatar
  • 4,389
14 votes
1 answer
13k views

Log Likelihood for GLM

library(bbmle) #successes in first column, failures in second Y <- matrix(c(1,2,4,3,2,0),3,2) #predictor X <- c(0,1,2) #use glm fit.glm <- glm(Y ~ X,family=binomial (link=logit)) summary(fit.glm) # …
Tom's user avatar
  • 1,202
13 votes

Probability that fewer than 24 people logging into the site will make a purchase

However, if (oblivious to a continuity correction) you take the key probability to be $P(X < 24),$ round excessively, and do a normal approximation to binomial using printed tables, you get $0.8264.$ …
BruceET's user avatar
  • 57.6k
13 votes

How to assess whether a coin tossed 900 times and comes up heads 490 times is biased?

Therefore, the number of heads thrown in 900 tries, $X$, has a ${\rm Binomial}(900,\frac{1}{2})$ distribution under the null hypothesis of a fair coin. … We know that the mass function for $ Y \sim {\rm Binomial}(n,p)$, is $$ P(Y = y) = \binom{n}{y} p^y (1-p)^{n-y} $$ I'll leave it to you to calculate $p$-value you seek. …
Macro's user avatar
  • 45.8k
12 votes

A meeting has 12 employees. Given that 8 of the employees are female, what is the probabilit...

.$$ Consequently, the number of females in the group has a binomial distribution: $$\dot{X} \equiv \sum_{i} X_i \sim \text{Bin}(12, \tfrac{1}{2}),$$ and the conditional probability of interest is: $$\mathbb …
Ben's user avatar
  • 133k

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