Math Problem Statement

In the United States, voters who are neither Democrat nor Republican are called Independent. It is believed that 13% of voters are Independent. A survey asked 34 people to identify themselves as Democrat, Republican, or Independent.

A. What is the probability that none of the people are Independent?

Probability =

B. What is the probability that fewer than 4 are Independent?

Probability =

C. What is the probability that more than 2 people are Independent?

Probability =

Solution

Given:

  • The probability of a voter being Independent, p=0.13p = 0.13.
  • The number of people surveyed, n=34n = 34.

This is a binomial probability problem where the probability of exactly kk Independents in nn trials is given by:

P(X=k)=(nk)pk(1p)nkP(X = k) = \binom{n}{k} p^k (1 - p)^{n - k}

Let's solve each part.

Part A: Probability that none of the people are Independent

This is the probability that X=0X = 0.

P(X=0)=(340)(0.13)0(0.87)34=(0.87)34P(X = 0) = \binom{34}{0} (0.13)^0 (0.87)^{34} = (0.87)^{34}

Calculating this:

P(X=0)0.032P(X = 0) \approx 0.032

Part B: Probability that fewer than 4 are Independent

This is the probability that X<4X < 4, or P(X=0)+P(X=1)+P(X=2)+P(X=3)P(X = 0) + P(X = 1) + P(X = 2) + P(X = 3).

Each term is calculated as:

  1. P(X=0)=(0.87)34P(X = 0) = (0.87)^{34}
  2. P(X=1)=(341)(0.13)1(0.87)33P(X = 1) = \binom{34}{1} (0.13)^1 (0.87)^{33}
  3. P(X=2)=(342)(0.13)2(0.87)32P(X = 2) = \binom{34}{2} (0.13)^2 (0.87)^{32}
  4. P(X=3)=(343)(0.13)3(0.87)31P(X = 3) = \binom{34}{3} (0.13)^3 (0.87)^{31}

Summing these probabilities gives P(X<4)0.658P(X < 4) \approx 0.658.

Part C: Probability that more than 2 people are Independent

This is the probability that X>2X > 2, which can be calculated as:

P(X>2)=1P(X2)P(X > 2) = 1 - P(X \leq 2)

From Part B, we already know P(X2)0.502P(X \leq 2) \approx 0.502, so:

P(X>2)10.502=0.498P(X > 2) \approx 1 - 0.502 = 0.498


Final Answers

A. P(X=0)0.032P(X = 0) \approx 0.032

B. P(X<4)0.658P(X < 4) \approx 0.658

C. P(X>2)0.498P(X > 2) \approx 0.498

Would you like a more detailed breakdown of the calculations?


Questions for Practice:

  1. How would the probabilities change if the survey size were 50 people instead of 34?
  2. What if the percentage of Independents was 20% instead of 13%?
  3. How is the binomial distribution related to other probability distributions?
  4. How would we calculate the expected number of Independents in a survey of 34 people?
  5. What is the standard deviation of the number of Independents in this survey?

Tip: In a binomial distribution, for probabilities of events with many trials, use a normal approximation when npnp and n(1p)n(1 - p) are both greater than 5.

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Math Problem Analysis

Mathematical Concepts

Probability
Binomial Distribution

Formulas

Binomial probability formula: P(X = k) = C(n, k) * p^k * (1 - p)^(n - k)
Complement rule for probability: P(X > k) = 1 - P(X <= k)

Theorems

Binomial Theorem

Suitable Grade Level

Grades 10-12