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If you toss two dice, what is the total number of ways in which you can obtain (a) a 12 and (b) a 7?

Short Answer

Expert verified
The total number of ways to get a 12 is 1, and to get a 7 is 6.

Step by step solution

01

Understanding a Dice Roll

A single die has 6 faces, with numbers 1 through 6. When two dice are rolled, each die operates independently of the other. The total number of outcomes for rolling two dice is the product of the number of outcomes for each die. Since each die has 6 faces, there are 6 x 6 = 36 possible outcomes when two dice are rolled.
02

Determining Ways to Get a Sum of 12

To obtain a sum of 12 from two dice, both dice must roll a 6. There is only one combination of dice that gives the sum of 12: (6,6).
03

Determining Ways to Get a Sum of 7

To obtain a sum of 7 from two dice, several combinations are possible. The combinations are (1,6), (2,5), (3,4), (4,3), (5,2), and (6,1). There are 6 different combinations that result in a sum of 7.

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Key Concepts

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

Dice Roll Outcomes
Understanding how to calculate outcomes of a dice roll is fundamental in the study of probability. Each die in a pair is an independent object, and the total outcomes can be found through simple multiplication of each die's possibilities. Rolling a single six-sided die, you have precisely 6 potential outcomes, numbered 1 to 6.

When rolling two dice, the number of outcomes for the first die (6 possibilities) multiplies with the number of outcomes for the second (also 6 possibilities), resulting in a total of 36 distinct possible outcomes. These outcomes range from the pair (1,1), which is the lowest, to (6,6), the highest. Each outcome is represented as a pair of numbers, where the first number corresponds to the outcome on the first die, and the second number represents the outcome on the second die.

It's important to consider this concept of independence and multiplication when approaching any problem involving multiple rolling dice, as it forms the basis of most probability calculations in such scenarios.
Probability Calculations
Probability calculations help us determine the likelihood of a particular event occurring out of all possible events. To find the probability of a certain outcome when rolling two dice, you divide the number of ways that outcome can occur by the total number of possible outcomes. The probability formula used within the context of dice rolling is:
\[ P(E) = \frac{\text{Number of favorable outcomes}}{\text{Total number of outcomes}} \]
For instance, there is only one way to roll a sum of 12 鈥 rolling two sixes 鈥 making the probability of this event:
\[ P(\text{sum of 12}) = \frac{1}{36} \].

Conversely, there are six different ways to roll a sum of 7, giving it a higher probability:
\[ P(\text{sum of 7}) = \frac{6}{36} = \frac{1}{6} \].

Thus, the probability of rolling a sum of 7 is much greater than that of rolling a sum of 12. This forms the core of probability calculations: counting the favorable outcomes and placing them in relation to the total number of outcomes.
Combinatorics
Combinatorics is a mathematical concept that deals with counting, arranging, and combination of elements in sets, particularly with finite sets. It is at the heart of calculating probabilities with dice. When we evaluate the number of ways to achieve a certain sum with two dice, we're using principles of combinatorics.

In our exercise, we've employed basic combinatorial reasoning to determine that there's only one combination to get a sum of 12, and six combinations to get a sum of 7. It's crucial to remember that the order of elements in the pairs for dice outcomes does matter, because a roll of (1,6) is different from a roll of (6,1), even though they result in the same sum. Therefore, when counting the combinations for sums, each unique pairing counts independently.

The more complex the dice problem, the more sophisticated combinatorial techniques we may need to use, such as permutations and variations. Coupled with a solid understanding of the fundamental counting principle, combinatorics enables us to tackle a wide variety of probability problems in a structured and methodical way.

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Most popular questions from this chapter

One of the most efficient heat engines ever built is a steam turbine in the Ohio valley, operating between \(430^{\circ} \mathrm{C}\) and \(1870^{\circ} \mathrm{C}\) on energy from West Virginia coal to produce electricity for the Midwest. (a) What is its maximum theoretical efficiency? (b) The actual efficiency of the engine is 42.0\(\%\) . How much useful power does the engine deliver if it takes in \(1.40 \times 10^{5} \mathrm{J}\) of energy each second from its hot reservoir?

An electric power plant that would make use of the temperature gradient in the ocean has been proposed. The system is to operate between \(20.0^{\circ} \mathrm{C}\) (surface water temperature) and \(5.00^{\circ} \mathrm{C}\) (water temperature at a depth of about 1 \(\mathrm{km}\) ). (a) What is the maximum efficiency of such a system? (b) If the useful power output of the plant is 75.0 MW, how much energy is taken in from the warm reservoir per hour? (c) In view of your answer to part (a), do you think such a system is worthwhile? Note that the 鈥渇uel鈥 is free.

Here is a clever idea. Suppose you build a two-engine device such that the exhaust energy output from one heat engine is the input energy for a second heat engine. We say that the two engines are running in series. Let \(e_{1}\) and \(e_{2}\) represent the efficiencies of the two engines. (a) The overall efficiency of the two-engine device is defined as the total work output divided by the energy put into the first engine by heat. Show that the overall efficiency is given by $$e=e_{1}+e_{2}-e_{1} e_{2}$$ (b) What If? Assume the two engines are Carnot engines. Engine 1 operates between temperatures \(T_{h}\) and \(T_{i} .\) The gas in engine 2 varies in temperature between \(T_{i}\) and \(T_{c} .\) In terms of the temperatures, what is the efficiency of the combination engine? (c) What value of the intermedone by temperature \(T_{i}\) will result in equal work being done by each of the two engines in series? (d) What value of \(T_{i}\) will result in each of the two engines in series having the same efficiency?

Two identically constructed objects, surrounded by thermal insulation, are used as energy reservoirs for a Carnot engine. The finite reservoirs both have mass \(m\) and specific heat \(c\) . They start out at temperatures \(T_{h}\) and \(T_{c}\) , where \(T_{h}>T_{c} .\) (a) Show that the engine will stop working when the final temperature of each object is \(\left(T_{h} T_{c}\right)^{1 / 2}\) (b) Show that the total work done by the Carnot engine is $$W_{\text { eng }}=m c\left(T_{h}^{1 / 2}-T_{c}^{1 / 2}\right)^{2}$$

Suppose a heat engine is connected to two energy reservoirs, one a pool of molten aluminum \(\left(660^{\circ} \mathrm{C}\right)\) and the other a block of solid mercury \(\left(-38.9^{\circ} \mathrm{C}\right)\) . The engine runs by freezing 1.00 \(\mathrm{g}\) of aluminum and melting 15.0 \(\mathrm{g}\) of mercury during each cycle. The heat of fusion of aluminum is \(3.97 \times 10^{5} \mathrm{J} / \mathrm{kg} ;\) the heat of fusion of mercury is \(1.18 \times 10^{4} \mathrm{J} / \mathrm{kg}\) . What is the efficiency of this engine?

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