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According to an Allstate/National Journal poll, \(39 \%\) of the U.S. adults polled said that it is extremely or very likely that "there will be a female president within \(10-15\) years" in the United States (USA Today, March 28,2012 ). Suppose that this percentage is true for the current population of U.S. adults. Find the probability that in a random sample of 800 U.S. adults, more than 330 would hold the foregoing belief.

Short Answer

Expert verified
The probability that more than 330 out of 800 U.S. adults would believe that 'there will be a female president within 10-15 years' is given by \( P_{>330} = 1 - P_{330} \), where \( P_{330} \) is the cumulative probability for 330 successes in 800 trials.

Step by step solution

01

Identify the parameters of the binomial distribution

The number \(n\) of trials is the size of the sample, which is 800. The probability \(p\) of success on any given trial is the proportion of U.S. adults that believe there will be a female president within 10-15 years, which is 0.39.
02

Identify the exact number for which we want the probability

We want to find the probability that more than 330 adults hold the belief, i.e. at least 331 adults. Therefore, we will calculate the cumulative probability for 330 adults and subtract it from 1.
03

Calculate the cumulative probability

The cumulative probability for \(k\) successes in \(n\) trials is given by the cumulative distribution function (CDF) of the binomial distribution: \[ P(X \le k) = \sum_{i=0}^{k}{{n}\choose{i}}\cdot p^i \cdot (1-p)^{n-i} \]Let's denote this probability as \( P_{330} \).
04

Calculate the desired probability

The probability of having more than 330 adults believing there will be a female president within 10-15 years, \( P_{>330} \), is given by:\[ P_{>330}=1-P_{330} \]

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Cumulative Distribution Function
The Cumulative Distribution Function (CDF) is a fundamental concept in probability and statistics that helps us understand the likelihood of a random variable falling within a specified range. In the context of a binomial distribution, the CDF provides the probability that a binomial random variable is less than or equal to a certain value.
Imagine you鈥檙e working with a large dataset and need to determine the probability of a specific outcome across multiple trials. The CDF simplifies this by summing up probabilities up to your point of interest.
For our problem, this means calculating the probability of having 330 or fewer U.S. adults, in a sample, believe in a female president's likelihood.
Using the formula:
  • \[ P(X \le k) = \sum_{i=0}^{k}{{n}\choose{i}}\cdot p^i \cdot (1-p)^{n-i} \]
We can identify the sum of probabilities from zero up to 330. This calculation can be complex by hand due to the number of terms involved, so statistical software or calculators often aid this process.
This CDF result is key for assessing the probability of more than 330 adults holding the belief, as it helps define the range of outcomes considered.鈥
Probability Calculation
Probability calculation in the context of the binomial distribution deals with determining how likely it is for a certain number of successes to occur in a series of trials.
In our scenario, the probability of success, or holding the belief, is 0.39 per individual adult, and we are looking at 800 trials or sampled adults.
This probability calculation involves determining how the probabilities of individual events (in this case, each adult's belief) accumulate across all trials.
The probability of more than 330 adults holding a particular belief is calculated by looking at the probability of 330 or fewer adults holding that belief and subtracting it from 1, i.e., the total certainty.
  • The formula used after calculating the CDF is: \[ P_{>330}=1-P_{330} \]
This approach shows how understanding cumulative probabilities helps identify the likelihood of surpassing a certain threshold.
In such scenarios, complementary probability results are crucial. Calculating probabilities for a range of values, instead of single value outcomes, provides clearer insights into the spread of data possibilities.
Statistics Problem Solving
Statistics problem solving often involves understanding the specific context and applying appropriate models to make predictions.
Here, the problem is getting to grips with how many people in a sample might share a belief.
To solve it effectively, we choose the binomial distribution because it models the number of successes in a fixed number of trials, considering two possible outcomes (here, believing or not believing in a female president in a 10-15 year timeframe).
By identifying the number of trials (800 adults) and the success probability (0.39), we use statistical methods to predict outcomes.
The use of the CDF in binomial distribution helps sum the probabilities for events less than or equal to a specific count. With this information, statistical problem-solving becomes a systematic process:
  • Define the parameters specific to the context
  • Use CDF and probability calculations to find total probabilities for desired outcomes
  • Subtract from 1 to find complementary probabilities where needed
This approach in statistics problem solving illustrates the value of analytical thinking combined with mathematical calculation to address real-world questions.

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Most popular questions from this chapter

Fast Auto Service guarantees that the maximum waiting time for its customers is 20 minutes for oil and lube service on their cars. It also guarantees that any customer who has to wait longer than 20 minutes for this service will receive a \(50 \%\) discount on the charges. It is estimated that the mean time taken for oil and lube service at this garage is 15 minutes per car and the standard deviation is \(2.4\) minutes. Suppose the time taken for oil and lube service on a car follows a normal distribution. a. What percentage of customers will receive a \(50 \%\) discount on their charges? b. Is it possible that it may take longer than 25 minutes for oil and lube service? Explain.

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