Exercise · ZW-BINOMIAL-DISTRIBUTION-008 · ★★☆ Intermediate
A binomial variable has mean 12 and variance 3. What are \(n\) and \(p\)?
Choose one option.
Show answer
- A. \(n=16,\ p=\tfrac34\)
Explanation
From \(np=12\) and \(np(1-p)=3\) we get \(1-p=\tfrac14\), so \(p=\tfrac34\) and \(n=16\). With \(p=\tfrac14\) the mean would be 4, not 12.
Review the concept: Binomial distribution
A binomial variable \(X\) counts the successes \(k\) in \(n\) independent Bernoulli trials with the same success probability \(p\); \(P(X=k)\) is the probability of getting \(k\) successes.
\[P(X=k)=\binom{n}{k}p^{k}(1-p)^{n-k},\quad k=0,1,\dots,n\]
More practice problems: binomial distribution
- ZW-BINOMIAL-DISTRIBUTION-001 A fair coin is tossed 4 times. What is the probability of getting exactly 2 heads?
- ZW-BINOMIAL-DISTRIBUTION-002 If X is binomial with n=20 and p=0.3, compute E[X].
- ZW-BINOMIAL-DISTRIBUTION-003 If X is binomial with n=20 and p=0.3, compute Var(X).
- ZW-BINOMIAL-DISTRIBUTION-004 A binomial variable has n=10 and p=0.1. What is P(X=0), rounded to 4 decimals?
- ZW-BINOMIAL-DISTRIBUTION-005 In which situation is the random variable binomial?
- ZW-BINOMIAL-DISTRIBUTION-006 A fair coin is tossed 3 times. What is the probability of getting at least one head?
- ZW-BINOMIAL-DISTRIBUTION-007 A die is rolled 6 times. What is the probability of getting exactly one 6?
- ZW-BINOMIAL-DISTRIBUTION-009 If X is binomial with n=10 and p=tfrac12, which probability equals P(X=3)?
← ZW-BINOMIAL-DISTRIBUTION-007 ZW-BINOMIAL-DISTRIBUTION-009 →