Math Problem Statement

United Airlines' flights from Boston to Seattle are on time 50% of the time. Suppose seven flights are randomly selected, and the number of on-time flights is recorded. Calculate the probabilities for different cases.

Solution

The problem involves calculating probabilities for a binomial distribution, as we are given a fixed number of trials (7 flights), with two possible outcomes (on time or not on time), and a constant probability of success (50% or 0.5 for an on-time flight).

Let:

  • n=7n = 7 (number of trials or flights),
  • p=0.5p = 0.5 (probability of success, i.e., flight being on time),
  • q=1p=0.5q = 1 - p = 0.5 (probability of failure, i.e., flight not being on time).

The binomial probability formula is: P(X=k)=(nk)pkqnkP(X = k) = \binom{n}{k} p^k q^{n-k} where kk is the number of on-time flights, and (nk)\binom{n}{k} is the binomial coefficient, or "n choose k."

1. The probability that at least 4 flights are on time:

This requires calculating P(X4)P(X \geq 4), which means the sum of the probabilities for 4, 5, 6, and 7 flights being on time: P(X4)=P(X=4)+P(X=5)+P(X=6)+P(X=7)P(X \geq 4) = P(X = 4) + P(X = 5) + P(X = 6) + P(X = 7)

2. The probability that at most 5 flights are on time:

This requires calculating P(X5)P(X \leq 5), which means the sum of the probabilities for 0 through 5 flights being on time: P(X5)=P(X=0)+P(X=1)+P(X=2)+P(X=3)+P(X=4)+P(X=5)P(X \leq 5) = P(X = 0) + P(X = 1) + P(X = 2) + P(X = 3) + P(X = 4) + P(X = 5)

3. The probability that exactly 2 flights are on time:

This is directly calculating P(X=2)P(X = 2) using the binomial probability formula.

Let me compute these probabilities for you.Here are the results:

  1. The probability that at least 4 flights are on time is 0.500.
  2. The probability that at most 5 flights are on time is 0.938.
  3. The probability that exactly 2 flights are on time is 0.164.

Would you like more details on any of these calculations or have any questions?

Here are 5 related questions to explore:

  1. What is the probability that all 7 flights are on time?
  2. How would the probabilities change if the success rate (on-time probability) was 60% instead of 50%?
  3. What is the expected number of on-time flights given the current probability?
  4. How would you calculate the standard deviation of the number of on-time flights?
  5. What is the probability that exactly 3 flights are on time?

Tip: Binomial distributions are useful when dealing with events that have a fixed number of trials, and each trial has only two possible outcomes.

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Math Problem Analysis

Mathematical Concepts

Probability
Binomial Distribution

Formulas

P(X = k) = (n choose k) * p^k * (1-p)^(n-k)
At least probability: P(X >= 4) = P(X = 4) + P(X = 5) + P(X = 6) + P(X = 7)
At most probability: P(X <= 5) = P(X = 0) + P(X = 1) + P(X = 2) + P(X = 3) + P(X = 4) + P(X = 5)
Exact probability: P(X = 2)

Theorems

Binomial Probability Theorem

Suitable Grade Level

Grades 10-12