/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 16 If you roll \(N\) dice, then the... [FREE SOLUTION] | 91Ó°ÊÓ

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If you roll \(N\) dice, then the probability \(p=p(N)\) that you will get exactly 4 sixes is given by $$ p=\frac{N(N-1)(N-2)(N-3)}{24} \times\left(\frac{1}{6}\right)^{4}\left(\frac{5}{6}\right)^{N-4} $$ a. What is the probability, rounded to three decimal places, of getting exactly 4 sixes if 10 dice are rolled? How many times out of 1000 rolls would you expect this to happen? b. How many dice should be rolled so that the probability of getting exactly 4 sixes is the greatest?

Short Answer

Expert verified
a. The probability is 0.054 and it occurs 54 times out of 1000 rolls. b. Roll 10 dice for the greatest probability.

Step by step solution

01

Substitute N for part (a)

To solve part (a), we first substitute \(N = 10\) into the probability formula:\[ p = \frac{10 \cdot 9 \cdot 8 \cdot 7}{24} \times \left(\frac{1}{6}\right)^4 \times \left(\frac{5}{6}\right)^{6} \]
02

Calculate combinatorial coefficient for part (a)

Calculate the first part of the equation:\[ \frac{10 \cdot 9 \cdot 8 \cdot 7}{24} = 210 \] Thus, the equation becomes:\[ p = 210 \times \left(\frac{1}{6}\right)^4 \times \left(\frac{5}{6}\right)^{6} \]
03

Calculate probability fractions for part (a)

Evaluate the fractions:\[ \left(\frac{1}{6}\right)^4 = \frac{1}{1296} \] and \[ \left(\frac{5}{6}\right)^{6} \approx 0.33489 \]
04

Compute probability for part (a)

Now calculate the probability:\[ p = 210 \times \frac{1}{1296} \times 0.33489 \approx 0.054264 \]Thus, the probability rounded to three decimal places is 0.054.
05

Expected occurrences out of 1000 for part (a)

To find how many times you expect this outcome in 1000 rolls, multiply the probability by 1000:\[ 0.054 \times 1000 = 54 \]Therefore, you would expect this to happen 54 times.
06

Maximize probability for part (b)

To find \(N\) that maximizes the probability, note that the second term \(\left(\frac{5}{6}\right)^{N-4}\) decreases with \(N\). Search for \(N\) values starting from 6 or higher since probability requires at least 4 dice to roll six: evaluate \(N = 8\), \(9\), and \(10\) and find the highest value of probability.
07

Trial calculations for part (b)

Calculate \(p(N)\) using steps 1-4 for different \(N\) values:- For \(N = 8\): \(p \approx 0.0075\)- For \(N = 9\): \(p \approx 0.0356\)- For \(N = 10\): \(p \approx 0.054\)Hence, the probability is greatest when \(N = 10\).

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Key Concepts

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

Combinatorial Probability
Understanding how combinatorial probability works is crucial when dealing with probability questions, especially those involving dice. This concept helps us figure out the number of ways events can occur. When rolling multiple dice, combinations come into play. For instance, in our example, we're interested in the number of ways to get exactly four sixes when rolling 10 dice.

The formula for combinations can be expressed \[ \binom{N}{k} = \frac{N!}{k!(N-k)!} \] where:
  • \(N!\) is the factorial of \(N\)
  • \(k!\) is the factorial of \(k\)
  • \(\binom{N}{k}\) indicates the number of ways to choose \(k\) successes out of \(N\) trials.
This part of the formula accounts for the number of ways you can arrange your desired outcomes - rolling four sixes among the ten dice, which is precisely what we solve using the term \(\frac{10 \cdot 9 \cdot 8 \cdot 7}{24}\) in the original solution.
Dice Probability
Dice probability is a particular application of basic probability principles. When you roll a fair die, the chance of landing a particular number, let's say a six, is one out of six because there are six possible outcomes.

In our problem, this simple probability is expressed as \(\left(\frac{1}{6}\right)\). When dealing with multiple rolls, you must consider the probability of rolling a six multiple times - exactly four times in this case.

Thus, we use \(\left(\frac{1}{6}\right)^{4}\), indicating that four dice show a six. This accounts for the exponential decrease in likelihood. Conversely, the expression \(\left(\frac{5}{6}\right)^{6}\) specifies the probability of the remaining dice not showing a six. Together, these components help calculate complex multistep outcomes.
Probability Calculation
Probability calculation is the heart of this exercise. Each step in solving the problem requires precise calculations. You first calculate possible combinations using factorials. This provides insights into the arrangement of successful and unsuccessful outcomes within your set of rolls.

Furthermore, calculating intermediate exponential probabilities, \(\left(\frac{1}{6}\right)^{4}\) and \(\left(\frac{5}{6}\right)^{6}\), is essential. These represent how likely certain numbers appear or don't, across multiple rolls.

Finally, multiplying all probability components together yields the comprehensive result. Here, you calculate \(210 \times \frac{1}{1296} \times 0.33489\), resulting in a probability of about 0.054. From this probability, deriving how often the event occurs in a set of trials makes practical application possible.
Binomial Probability
Binomial probability is a specialized form of calculating the probability involving two possible outcomes - success or failure - in repeated, independent trials. Here, success is rolling a six, and failure is rolling any other number.

The binomial distribution, given by: \[ P(X=k) = \binom{n}{k} p^{k} (1-p)^{n-k} \]concerns how often a specified number of successes, \(k\), appears across \(n\) trials.

Our scenario involves computing the probability of exactly four successes (rolling a six) among ten tries (dice). The binomial formula fits perfectly here, as it uses the probability of one success (a single die showing a six) and multiple failures (other dice showing different numbers) to calculate the likelihood of our specific outcome happening.

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Most popular questions from this chapter

A child has 64 blocks that are 1 -inch cubes. She wants to arrange the blocks into a solid rectangle \(h\) blocks long and \(w\) blocks wide. There is a relationship between \(h\) and \(w\) that is determined by the restriction that all 64 blocks must go into the rectangle. A rectangle \(h\) blocks long and \(w\) blocks wide uses a total of \(h \times w\) blocks. Thus \(h w=64\). Applying some elementary algebra, we get the relationship we need: $$ w=\frac{64}{h} . $$ a. Use a formula to express the perimeter \(P\) in terms of \(h\) and \(w\). b. Using Equation (2.3), find a formula that expresses the perimeter \(P\) in terms of the height only. c. How should the child arrange the blocks if she wants the perimeter to be the smallest possible? d. Do parts \(b\) and \(c\) again, this time assuming that the child has 60 blocks rather than 64 blocks. In this situation the relationship between \(h\) and \(w\) is \(w=60 / h\). (Note: Be careful when you do part c. The child will not cut the blocks into pieces!)

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