Math Problem Statement
A pharmaceutical company knows that five percent of all users of a certain drug experience a serious side effect. A researcher examines a sample of 340 users of the drug.
- What is the probability of finding between 8 and 12 cases with side effects?
- What is the probability of finding more than 16 cases with side effects?
Solution
This problem can be solved using the binomial distribution, since we are dealing with a fixed number of trials (340 users), two possible outcomes (side effect or no side effect), and a constant probability of a side effect occurring (5% or 0.05).
1. Probability of finding between 8 and 12 cases with side effects
Let's define:
- (the number of users in the sample)
- (the probability of a serious side effect for each user)
- is a binomial random variable representing the number of users who experience side effects.
We are asked to find , which can be calculated as:
Each term can be computed using the binomial probability formula:
Where:
- is the binomial coefficient
- is the probability of users having side effects
- is the probability of the remaining users not having side effects.
However, given the large number of trials, it is more efficient to use the normal approximation to the binomial distribution. The normal approximation is valid because and are both sufficiently large (which is true in this case, since ).
Step 1: Apply the normal approximation to the binomial distribution
For a binomial distribution , the normal approximation gives us:
Where:
- (mean)
- (standard deviation)
Step 2: Use continuity correction
To approximate the probability , we use continuity correction by adjusting the values by . So we calculate:
This becomes:
Using a standard normal distribution table or a calculator:
Thus:
So, the probability of finding between 8 and 12 cases with side effects is approximately 0.1205 (or 12.05%).
2. Probability of finding more than 16 cases with side effects
We need to calculate .
Using the normal approximation with continuity correction, we calculate:
This becomes:
From the standard normal distribution table:
Thus, the probability of finding more than 16 cases with side effects is approximately 0.5517 (or 55.17%).
Would you like more details on any part of the calculations, or do you have any further questions?
Follow-up questions:
- What is the binomial coefficient, and how is it calculated?
- How does the normal approximation to the binomial distribution work?
- Why is a continuity correction necessary in normal approximation?
- What are the conditions for the normal approximation to be valid for binomial problems?
- How does the shape of a binomial distribution change as approaches 0 or 1?
Tip:
When using the normal approximation for binomial distributions, always ensure that and are both greater than 5 for an accurate approximation.
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Math Problem Analysis
Mathematical Concepts
Binomial Distribution
Normal Approximation
Probability
Formulas
P(X = k) = (n choose k) * p^k * (1 - p)^(n - k)
Normal approximation: X ~ N(np, np(1 - p))
Z = (X - μ) / σ
Theorems
Central Limit Theorem
Continuity Correction
Suitable Grade Level
College level (Probability & Statistics)
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