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An experiment is given together with an event. Find the (modeled) probability of each event, assuming that the coins and dice are distinguishable and fair, and that what is observed are the faces or numbers uppermost. Two dice are rolled; the numbers add to 9 .

Short Answer

Expert verified
The probability of the sum of two dice rolls being equal to 9 is \(\frac{1}{9}\), as there are 4 favourable outcomes out of a total of 36 possible outcomes.

Step by step solution

01

Determine all possible outcomes of rolling two dice

Since there are two dice with 6 faces each, there are a total of 6 x 6 = 36 possible outcomes when rolling the dice.
02

List the combinations where the sum is equal to 9

We'll now list all the possible pairs of dice rolls that sum up to 9: 1. (3, 6) 2. (4, 5) 3. (5, 4) 4. (6, 3) There are 4 combinations where the sum of the two dice rolls is equal to 9.
03

Calculate the probability of the event

To find the probability of the event, we will divide the number of favourable outcomes (dice roll combinations summing to 9) by the total number of possible outcomes (all dice roll combinations). Probability = \(\frac{4}{36}\) To simplify this fraction, we divide both the numerator and the denominator by 4: Probability = \(\frac{1}{9}\)
04

Write the final answer

The probability of the sum of the two dice rolls being equal to 9 is \(\frac{1}{9}\).

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Key Concepts

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

Rolling Dice
Rolling dice is a fundamental experiment in probability theory that serves as a classic example to illustrate various probabilistic principles. When you roll a die, you are essentially throwing it to see which numbered side will land face up. This is considered a fair random experiment because each face of the die has an equal chance of landing face up. A standard die is a six-sided cube with numbers ranging from 1 to 6 on each face.

When rolling two dice, we can think of each die as a separate experiment. The outcome of the whole roll is thus a combination of two separate results: the result from the first die and the result from the second die. There are multiple ways to roll these two dice, which brings us to the heart of understanding probability in dice games.
Combinatorics
Combinatorics is the branch of mathematics dealing with combinations and permutations of objects. It becomes crucial when evaluating outcomes in probability problems like rolling dice. With combinatorics, we calculate how many different ways we can arrange our outcomes.

When rolling two dice, each die has 6 possible numbers that could appear on its top face, making it 6 choices per die. Combinatorics tells us that by multiplying these choices, we find the total number of possible outcomes. Therefore, there are 6 x 6 = 36 possible outcomes when rolling two dice.

In the context of probability exercises, combinatorics provides the tools necessary to find and list all the outcomes that fit specific criteria, such as a total sum from the two dice.
Favorable Outcomes
In probability theory, favorable outcomes refer to the specific outcomes of an experiment that fulfill the conditions of an event we're interested in. When rolling two dice and aiming for their sum to be 9, the favorable outcomes are those rolls where the numbers on the dice add up to 9.

To determine these outcomes, we list combinations from all possible results. For two dice summing to 9, the combinations are (3, 6), (4, 5), (5, 4), and (6, 3). This means there are 4 favorable outcomes in our problem.

To calculate the probability of achieving these favorable outcomes, we divide the number of favorable outcomes by the total number of possible outcomes (36 in this case). This gives us the probability of the event occurring, and helps us understand how often we can expect this outcome in repeated experiments.

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Most popular questions from this chapter

An experiment is given together with an event. Find the (modeled) probability of each event, assuming that the coins and dice are distinguishable and fair, and that what is observed are the faces or numbers uppermost. Three coins are tossed; the result is at most one head.

Use counting arguments from the preceding chapter. Horse Races The seven contenders in the fifth horse race at Aqueduct on February 18,2002, were: Pipe Bomb, Expect a Ship, All That Magic, Electoral College, Celera, Cliff Glider, and Inca Halo. \({ }^{5}\) You are interested in the first three places (winner, second place, and third place) for the race. a. Find the cardinality \(n(S)\) of the sample space \(S\) of all possible finishes of the race. (A finish for the race consists of a first, second, and third place winner.) b. Let \(E\) be the event that Electoral College is in second or third place, and let \(F\) be the event that Celera is the winner. Express the event \(E \cap F\) in words, and find its cardinality.

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Explain how the property \(P\left(A^{\prime}\right)=1-P(A)\) follows directly from the properties of a probability distribution.

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