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A company that produces fine crystal knows from experience that \(10 \%\) of its goblets have cosmetic flaws and must be classified as "seconds." a. Among six randomly selected goblets, how likely is it that only one is a second? b. Among six randomly selected goblets, what is the probability that at least two are seconds? c. If goblets are examined one by one, what is the probability that at most five must be selected to find four that are not seconds?

Short Answer

Expert verified
a. 0.3543 b. 0.1143 c. 0.9185

Step by step solution

01

Define the Problem

We are given that the probability of a goblet having a cosmetic flaw is 0.10. We need to use this information to solve a binomial probability problem where the trials are independent, and each goblet has a probability of either being a second (having a cosmetic flaw) or not.
02

Part a - Calculate the Probability of Exactly One Flawed Goblet

The number of trials, n, is 6, and the probability of success (a flawed goblet) p is 0.10. We want to find the probability of exactly one flawed goblet among six.The formula for the probability of exactly k successes in n binomial trials is given by:\[P(X = k) = \binom{n}{k} p^k (1-p)^{n-k}\]Applying values, \( k = 1 \), \( n = 6 \), and \( p = 0.10 \):\[P(X = 1) = \binom{6}{1} (0.10)^1 (0.90)^5 = 6 \times 0.10 \times 0.59049 = 0.354294\]
03

Part b - Calculate the Probability of At Least Two Flawed Goblets

We want to find the probability that at least two goblets are seconds, which is equivalent to finding 1 minus the probability of 0 or 1 goblet.\[P(X \geq 2) = 1 - (P(X = 0) + P(X = 1))\]First, calculate \( P(X = 0) \):\[P(X = 0) = \binom{6}{0} (0.10)^0 (0.90)^6 = 1 \times 0.531441 = 0.531441\]Using \( P(X = 1) = 0.354294 \) from Part a, calculate:\[P(X \geq 2) = 1 - (0.531441 + 0.354294) = 1 - 0.885735 = 0.114265\]
04

Part c - Probability of Finding Four Non-Seconds in Five Trials

Here, we need the probability of finding at most one flawed goblet among five to ensure four are not seconds. The probability of a goblet not being a second is 0.90.\[P(\text{at most 1 second in 5 trials}) = P(X = 0) + P(X = 1)\]Calculated as:\[P(X = 0) = \binom{5}{0} (0.10)^0 (0.90)^5 = 1 \times 0.59049 = 0.59049\]\[P(X = 1) = \binom{5}{1} (0.10)^1 (0.90)^4 = 5 \times 0.10 \times 0.6561 = 0.32805\]Add both probabilities:\[P(\text{at most 1 second}) = 0.59049 + 0.32805 = 0.91854\]
05

Conclusion

Calculate and combine the results. In Part a, the probability of exactly one flawed goblet is 0.354294. In Part b, the probability of at least two flawed goblets is 0.114265. In Part c, the probability that only five are needed to find four non-seconds is 0.91854.

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Key Concepts

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

Probability of Success
In binomial probability, the term 'probability of success' refers to the likelihood of a single trial resulting in a desired outcome. This is denoted by the symbol \( p \). In the context of our crystal goblet problem, the success is defined as selecting a goblet with a cosmetic flaw. The company has determined that each goblet has a \( 10\% \) chance of having a flaw. Therefore, the probability of success \( p \) is \( 0.10 \).

This probability remains constant for every goblet you examine since each one is independent of the others. Therefore, regardless of how many goblets you select, the chance of finding one with a defect is always \( 0.10 \). This uniform probability is foundational to solving binomial probability problems. The real challenge comes when you need to calculate the probability of multiple successes across several trials.

Understanding this concept allows us to use the binomial formula effectively to find probabilities for different scenarios, such as exactly one goblet being flawed among six or finding at least two flawed goblets.
Binomial Trials
Binomial trials refer to experiments that have a fixed number of repeated trials with two possible outcomes for each trial: success or failure. In our exercise involving goblets, each time we select a goblet, either it will be classified as a 'second' (success) if it has a flaw, or it will not (failure).

When solving for this type of problem, we often employ the binomial probability formula, which helps determine the probability of a certain number of successes in a given set of trials. The formula is: \[P(X = k) = \binom{n}{k} p^k (1-p)^{n-k}\]where:
  • \( n \) is the total number of trials (e.g., 6 goblets selected)
  • \( k \) is the number of successes we are interested in (e.g., exactly one flawed goblet)
  • \( p \) is the probability of success on a single trial
  • \( 1-p \) is the probability of failure
The binomial coefficient \( \binom{n}{k} \) calculates the number of ways to pick \( k \) successes out of \( n \) trials. This concept helps us understand how to approach varying situations, such as in part a, where we calculate the probability of exactly one goblet being flawed.
Independent Events
In probability, independent events are events where the occurrence of one does not affect the occurrence of another. This is crucial in our goblet problem because the state of one goblet (whether flawed or not) does not impact the state of another. Each selection is an independent event.

For example, if you have already selected one flawed goblet, the probability of the next having a flaw remains \( 0.10 \). This independence is fundamental to the application of the binomial distribution. It allows each trial to be considered separately, maintaining a consistent probability of success throughout.

This property of independence is important when combining probabilities for multiple scenarios, such as calculating the probability of several different outcomes. It simplifies the computation as each selection is a fresh, independent event. Recognizing this allows for the combination of probabilities to find the answer to parts like b and c, where you calculate the probability of multiple successes in sequential trials.

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