Binomial Distribution

203 questions · 25 question types identified

Direct binomial probability calculation

Questions that directly give n and p and ask for P(X = k), P(X ≤ k), or P(X ≥ k) with no additional context or multi-part scenarios.

31
15.3% of questions
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1 In a certain country \(12 \%\) of houses have solar heating. 19 houses are chosen at random. Find the probability that fewer than 4 houses have solar heating.
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Probability of range of values

Find P(a ≤ X ≤ b) or P(a < X < b) for a binomial random variable, requiring subtraction of cumulative probabilities.

21
10.3% of questions
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1 Biscuits are sold in packets of 18. There is a constant probability that any biscuit is broken, independently of other biscuits. The mean number of broken biscuits in a packet has been found to be 2.7 . Find the probability that a packet contains between 2 and 4 (inclusive) broken biscuits.
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Identify distribution and parameters

Questions that ask students to state or suggest a suitable binomial distribution model including specific parameter values for a given context.

18
8.9% of questions
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7. Emma throws a fair coin 15 times and records the number of times it shows a head.
a State the appropriate distribution to model the number of times the coin shows a head giving any relevant parameter values.
b Find the probability that Emma records:
i exactly 8 heads
ii at least 4 heads.
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Finding binomial parameters from properties

Determine n or p given information about mean, variance, or specific probabilities like P(X = 0) or mode.

17
8.4% of questions
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11 The random variable \(X\) is such that \(X \sim \mathrm {~B} ( n , p )\)
The mean value of \(X\) is 225 The variance of \(X\) is 144 Find \(p\).
Circle your answer.
0.36
0.6
0.64
0.8
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Single batch expected count

Calculate expected number of occurrences across multiple independent repetitions of a single binomial experiment (e.g., expected number of samples with a specific outcome across many samples).

14
6.9% of questions
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2 A normal pack of 52 playing cards contains 4 aces. A card is drawn at random from the pack. It is then replaced and the pack is shuffled, after which another card is drawn at random.
  1. Find the probability that neither card is an ace.
  2. This process is repeated 10 times. Find the expected number of times for which neither card is an ace.
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Verify conditions in context

Questions that ask students to state assumptions or verify conditions for a specific given scenario to be modeled by a binomial distribution.

11
5.4% of questions
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15 (e) State two necessary assumptions in context so that the distribution stated in part (a) is valid.
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Independent binomial samples with compound probability

Calculate the probability that a certain number of independent binomial samples satisfy a given condition (e.g., exactly 2 out of 3 periods have at least one success).

11
5.4% of questions
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2. The probability of a bolt being faulty is 0.3 . Find the probability that in a random sample of 20 bolts there are
  1. exactly 2 faulty bolts,
  2. more than 3 faulty bolts. These bolts are sold in bags of 20. John buys 10 bags.
  3. Find the probability that exactly 6 of these bags contain more than 3 faulty bolts.
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Multiple independent binomial calculations

Questions involving several people/groups each with their own binomial distribution, or multiple separate binomial probability calculations in different parts (e.g., boys and girls with different probabilities, or different days with different probabilities).

10
4.9% of questions
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3 Visitors to a Wildlife Park in Africa have independent probabilities of 0.9 of seeing giraffes, 0.95 of seeing elephants, 0.85 of seeing zebras and 0.1 of seeing lions.
  1. Find the probability that a visitor to the Wildlife Park sees all these animals.
  2. Find the probability that, out of 12 randomly chosen visitors, fewer than 3 see lions.
  3. 50 people independently visit the Wildlife Park. Find the mean and variance of the number of these people who see zebras.
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Combined probability with other distributions

Solve problems involving binomial distribution combined with other probability concepts like conditional probability or tree diagrams.

9
4.4% of questions
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3 An auction house offers items of jewellery for sale at its public auctions. Each item has a reserve price which is less than the lower price estimate which, in turn, is less than the upper price estimate. The outcome for any item is independent of the outcomes for all other items. The auction house has found, from past records, the following probabilities for the outcomes of items of jewellery offered for sale.
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Basic E(X) and Var(X) calculation

Questions that ask directly for the mean and/or variance of a binomial distribution X ~ B(n,p), or simple linear transformations Y = aX + b, without requiring probability calculations.

8
3.9% of questions
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1 A fair coin is tossed 5 times and the number of heads is recorded.
  1. The random variable \(X\) is the number of heads. State the mean and variance of \(X\).
  2. The number of heads is doubled and denoted by the random variable \(Y\). State the mean and variance of \(Y\).
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Geometric distribution (first success)

Find the probability that the first success occurs on a specific trial, or before/after a certain trial.

6
3.0% of questions
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  1. A fair coin is tossed 4 times.
Find the probability that
  1. an equal number of head and tails occur
  2. all the outcomes are the same,
  3. the first tail occurs on the third throw.
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State general binomial conditions

Questions that ask students to state or list the general conditions required for a binomial distribution without reference to a specific context.

6
3.0% of questions
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6
  1. State three conditions that must be satisfied for a situation to be modelled by a binomial distribution. On any day, there is a probability of 0.3 that Julie's train is late.
  2. Nine days are chosen at random. Find the probability that Julie's train is late on more than 7 days or fewer than 2 days.
  3. 90 days are chosen at random. Find the probability that Julie's train is late on more than 35 days or fewer than 27 days.
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At least one success

Finding minimum n such that P(X ≥ 1) exceeds a threshold, typically solved using P(X ≥ 1) = 1 - P(X = 0) = 1 - (1-p)^n.

6
3.0% of questions
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3 The probability that Janice will buy an item online in any week is 0.35 . Janice does not buy more than one item online in any week.
  1. Find the probability that, in a 10 -week period, Janice buys at most 7 items online.
  2. The probability that Janice buys at least one item online in a period of \(n\) weeks is greater than 0.99 . Find the smallest possible value of \(n\).
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General probability threshold

Finding minimum or maximum n for other probability conditions (e.g., P(X < r) < k, P(X = 0) ≥ k, or mean requirements), requiring cumulative binomial calculations or inequalities.

6
3.0% of questions
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3 In a large consignment of mangoes, 15\% of mangoes are classified as small, 70\% as medium and \(15 \%\) as large.
  1. Yue-chen picks 14 mangoes at random. Find the probability that fewer than 12 of them are medium or large.
  2. Yue-chen picks \(n\) mangoes at random. The probability that none of these \(n\) mangoes is small is at least 0.1 . Find the largest possible value of \(n\).
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Normal approximation to binomial

Use normal distribution with continuity correction to approximate binomial probabilities for large n.

5
2.5% of questions
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5 On average, \(34 \%\) of the people who go to a particular theatre are men.
  1. A random sample of 14 people who go to the theatre is chosen. Find the probability that at most 2 people are men.
  2. Use an approximation to find the probability that, in a random sample of 600 people who go to the theatre, fewer than 190 are men.
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Probability distribution table

Complete or construct the full probability distribution table for a binomial or related discrete random variable.

5
2.5% of questions
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3. In a town, \(30 \%\) of residents listen to the local radio station. Four residents are chosen at random.
  1. State the distribution of the random variable \(X\), the number of these four residents that listen to local radio.
  2. On graph paper, draw the probability distribution of \(X\).
  3. Write down the most likely number of these four residents that listen to the local radio station.
  4. Find \(\mathrm { E } ( X )\) and \(\operatorname { Var } ( X )\).
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Sum or combination of independent binomial values

Find probabilities involving the sum or combined outcomes of multiple independent values drawn from the same binomial distribution (e.g., sum of two values equals a target).

4
2.0% of questions
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3 A random variable \(X\) has the distribution \(\mathrm { B } ( 13,0.12 )\).
  1. Find \(\mathrm { P } ( X < 2 )\). Two independent values of \(X\) are found.
  2. Find the probability that exactly one of these values is equal to 2 .
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E(X) and Var(X) with probability calculations

Questions that require calculating both probabilities (using binomial formula or tables) and expected value/variance in the same problem, typically in multi-part questions.

3
1.5% of questions
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14 The random variable \(T\) follows a binomial distribution where $$T \sim \mathrm {~B} ( 16,0.3 )$$ The mean of \(T\) is denoted by \(\mu\).
14
  1. \(\quad\) Find \(\mathrm { P } ( T \leq \mu )\).
    14
  2. Find the variance of \(T\).
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Nested binomial expected count

Calculate expected count where the event of interest is defined by a binomial probability within each batch, then count across multiple batches (e.g., expected number of boxes containing exactly k items with a property).

3
1.5% of questions
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5 Screws are sold in packets of 15. Faulty screws occur randomly. A large number of packets are tested for faulty screws and the mean number of faulty screws per packet is found to be 1.2 .
  1. Show that the variance of the number of faulty screws in a packet is 1.104 .
  2. Find the probability that a packet contains at most 2 faulty screws. Damien buys 8 packets of screws at random.
  3. Find the probability that there are exactly 7 packets in which there is at least 1 faulty screw.
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Two-stage binomial problems

Problems where a binomial outcome determines parameters for a second binomial experiment.

2
1.0% of questions
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7. A biased spinner can only land on one of the numbers \(1,2,3\) or 4 . The random variable \(X\) represents the number that the spinner lands on after a single spin and \(\mathrm { P } ( X = r ) = \mathrm { P } ( X = r + 2 )\) for \(r = 1,2\) Given that \(\mathrm { P } ( X = 2 ) = 0.35\)
  1. find the complete probability distribution of \(X\). Ambroh spins the spinner 60 times.
  2. Find the probability that more than half of the spins land on the number 4 Give your answer to 3 significant figures.
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Most likely value (mode)

Find the value of X with highest probability, often the value closest to the mean.

2
1.0% of questions
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2.The discrete random variable \(X\) follows the binomial distribution $$X \sim \mathrm {~B} ( n , p )$$ where \(0 < p < 1\) .The mode of \(X\) is \(m\) .
(a)Write down,in terms of \(m , n\) and \(p\) ,an expression for \(\mathrm { P } ( X = m )\)
(b)Determine,in terms of \(n\) and \(p\) ,an interval of width 1 ,in which \(m\) lies.
(c)Find a value of \(n\) where \(n > 100\) ,and a value of \(p\) where \(p < 0.2\) ,for which \(X\) has two modes. For your chosen values of \(n\) and \(p\) ,state these two modes.
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Binomial with derived parameters

Questions where n or p must be derived from given information (e.g., 'average number of 5s was 4.8' to find p, or 'mean number of defectives is 1.6' in packs of 20) before calculating probabilities.

2
1.0% of questions
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1 The mean number of defective batteries in packs of 20 is 1.6 . Use a binomial distribution to calculate the probability that a randomly chosen pack of 20 will have more than 2 defective batteries.
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Proof and derivation of E(X) and Var(X)

Questions requiring formal proof from first principles of the binomial mean and variance formulas, or deriving variance using E(X(X-1)).

2
1.0% of questions
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11 The random variable \(X\) takes the value 1 with probability \(p\) and the value 0 with probability \(1 - p\).
  1. Find each of the following.
    • \(\mathrm { E } ( X )\)
    • \(\operatorname { Var } ( X )\)
    • The random variable \(Y \sim \mathrm {~B} ( 50,0.2 )\) has mean \(\mu\) and variance \(\sigma ^ { 2 }\).
    Use the results of part (a) to prove that
    • \(\mu = 10\)
    • \(\sigma ^ { 2 } = 8\).
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Binomial with complementary events

Questions where the binomial setup involves calculating probabilities for complementary scenarios or 'at least one' type problems that require understanding of complement rule in the context setup.

1
0.5% of questions
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4 A game for two players is played using a fair 4-sided dice with sides numbered 1, 2, 3 and 4. One turn consists of throwing the dice repeatedly up to a maximum of three times. When a 4 is obtained, no further throws are made during that turn. A player who obtains a 4 in their turn scores 1 point.
  1. Show that the probability that a player obtains a 4 in one turn is \(\frac { 37 } { 64 }\).
    Xeno and Yao play this game.
  2. Find the probability that neither Xeno nor Yao score any points in their first two turns.
  3. Xeno and Yao each have three turns. Find the probability that Xeno scores 2 more points than Yao.
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Sum or product of binomial variables

Find probabilities or distributions involving sums, products, or other combinations of independent binomial random variables.

0
0.0% of questions