Math Problem Statement

Suppose
60 % of people like balloons.

In a random sample of 102 people what is the probability that between 58 and 63 of them like balloons?

More precisely, let X be the random variable that counts how many people in samples of size n = 102 like balloons. Find
P ( 58 ≤ X ≤ 63 ) .

Give your answer as a decimal number between 0 and 1, accurate to at least 4 decimal places (something like 0.1234). Put your answer in the answer box.

Solution

To solve this, we can model the number of people who like balloons as a binomial random variable. The binomial distribution is appropriate because each person is independent, and they can either like balloons (with probability p=0.60p = 0.60) or not like them (with probability 1p=0.401 - p = 0.40).

Given:

  • n=102n = 102 (sample size),
  • p=0.60p = 0.60 (probability a person likes balloons),
  • We need to find P(58X63)P(58 \leq X \leq 63), where XX is the number of people in the sample who like balloons.

Step 1: Approximate the Binomial Distribution with a Normal Distribution

For large nn, we can use the normal approximation to the binomial distribution, which is typically accurate when nn is large and pp is not too close to 0 or 1.

The parameters for the normal distribution approximation are:

  • Mean μ=np=102×0.60=61.2\mu = np = 102 \times 0.60 = 61.2
  • Standard deviation σ=np(1p)=102×0.60×0.40=24.484.948\sigma = \sqrt{np(1-p)} = \sqrt{102 \times 0.60 \times 0.40} = \sqrt{24.48} \approx 4.948

Step 2: Apply the Continuity Correction

Since we're using a continuous distribution (normal) to approximate a discrete one (binomial), we apply a continuity correction by adjusting the values for the desired range:

  • For X58X \geq 58, we use 57.557.5 (i.e., 580.558 - 0.5).
  • For X63X \leq 63, we use 63.563.5 (i.e., 63+0.563 + 0.5).

Thus, we need to compute P(57.5X63.5)P(57.5 \leq X \leq 63.5).

Step 3: Convert to Standard Normal Distribution (Z-Scores)

We convert these values into standard normal ZZ-scores using the formula:

Z=XμσZ = \frac{X - \mu}{\sigma}

For X=57.5X = 57.5: Z1=57.561.24.9483.74.9480.747Z_1 = \frac{57.5 - 61.2}{4.948} \approx \frac{-3.7}{4.948} \approx -0.747

For X=63.5X = 63.5: Z2=63.561.24.9482.34.9480.464Z_2 = \frac{63.5 - 61.2}{4.948} \approx \frac{2.3}{4.948} \approx 0.464

Step 4: Use the Standard Normal Distribution Table or a Calculator

Now, we use the standard normal table or a calculator to find the cumulative probabilities corresponding to these ZZ-scores.

  • P(Z0.747)0.2276P(Z \leq -0.747) \approx 0.2276
  • P(Z0.464)0.6772P(Z \leq 0.464) \approx 0.6772

Step 5: Calculate the Desired Probability

The probability that XX is between 58 and 63 is the difference between these cumulative probabilities:

P(58X63)=P(Z0.464)P(Z0.747)=0.67720.2276=0.4496P(58 \leq X \leq 63) = P(Z \leq 0.464) - P(Z \leq -0.747) = 0.6772 - 0.2276 = 0.4496

Final Answer:

The probability that between 58 and 63 people like balloons is approximately 0.4496.

Would you like further details or explanations on any part of this? Here are a few related questions:

  1. How do we calculate the mean and standard deviation for a binomial distribution?
  2. Why is the continuity correction necessary in normal approximation?
  3. What are the conditions for using the normal approximation to the binomial distribution?
  4. How do we use the Z-score to find probabilities in a normal distribution?
  5. Can this problem be solved directly using the binomial distribution instead of normal approximation?

Tip: When using the normal approximation, check that npnp and n(1p)n(1-p) are both greater than 5 to ensure the approximation is valid.

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Math Problem Analysis

Mathematical Concepts

Binomial Distribution
Normal Approximation to Binomial Distribution
Z-Scores
Probability Theory

Formulas

P(X ≤ x) = P(Z ≤ (x - μ) / σ)
μ = np
σ = sqrt(np(1-p))

Theorems

Central Limit Theorem
Normal Approximation to the Binomial Distribution

Suitable Grade Level

Grades 11-12