Question

A slot machine has three wheels that spin independently. Each has 10 equally likely symbols: 4 bars, 3 lemons, 2 cherries, and a bell. If you play, what is the probability that a) you get 3 lemons? b) you get no fruit symbols? c) you get 3 bells (the jackpot)? d) you get no bells?

Short answer

a) 0.027, b) 0.125, c) 0.001, d) 0.729

Step-by-step solution

Understanding the Problem

To solve this problem, we need to calculate probabilities involving three wheels with 10 symbols each: 4 bars, 3 lemons, 2 cherries, and 1 bell. These probabilities depend on the combination of symbols obtained on all three wheels.

Probability of Getting 3 Lemons

Each wheel has 3 lemons out of 10 symbols, so the probability of getting a lemon on one wheel is \( \frac{3}{10} \). The probability that all three wheels show a lemon is \( \left( \frac{3}{10} \right)^3 = \frac{27}{1000} \).

Probability of Getting No Fruit Symbols

The problem defines fruit symbols as lemons or cherries (3 lemons + 2 cherries = 5 fruits). The probability of getting a non-fruit symbol (4 bars + 1 bell) on one wheel is \( \frac{5}{10} = \frac{1}{2} \). For all three wheels, this is \( \left( \frac{1}{2} \right)^3 = \frac{1}{8} \).

Probability of Getting 3 Bells

Each wheel has 1 bell, so the probability of getting a bell on one wheel is \( \frac{1}{10} \). The probability of getting a bell on all three wheels (jackpot) is \( \left( \frac{1}{10} \right)^3 = \frac{1}{1000} \).

Probability of Getting No Bells

The probability of not getting a bell on one wheel is \( \frac{9}{10} \). The probability that none of the three wheels gets a bell is \( \left( \frac{9}{10} \right)^3 = \frac{729}{1000} \).

Key concepts

Combinatorics

Combinatorics is a branch of mathematics that deals with counting, combinations, and permutations. In the context of probability, it helps us to determine the total number of possible outcomes of an event. When considering a slot machine with three wheels, each wheel having 10 symbols that spin independently, we must first understand the various combinations possible. This is a classic example of applying combinatorics to compute the probabilities of different outcomes.

In our specific problem, each wheel has the following symbols: 4 bars, 3 lemons, 2 cherries, and 1 bell. These symbols represent different potential outcomes, and combinatorics helps us figure out how likely certain combinations are. For example, when calculating the probability of all three wheels landing on a particular combination of symbols, we utilize the basic principles of combinatorics to count the number of favorable outcomes versus the total possible outcomes.

It's essential to note that these wheels are independent, meaning the outcome of one does not affect the others. Thus, we can multiply the probabilities of individual outcomes on each wheel to get the total probability for a particular combination.

Independent Events

Independent events in probability theory are events where the occurrence of one does not affect the occurrence of others. Understanding independence is crucial when computing probabilities for our slot machine problem.

In our scenario, each spin of a wheel is an independent event. The outcome of one wheel does not influence the others, allowing us to calculate the probability of events on one wheel separately from the others. For example, if one wheel results in a lemon, this has no bearing on whether the next wheel will also display a lemon.

To find the probability of getting a combination, such as three lemons, you multiply the independent probability of getting a lemon on a single wheel by itself twice more since you have three wheels. This multiplication is a key feature of independent events:

• Probability of lemon on one wheel: \( \frac{3}{10} \)
• Probability of three lemons (all wheels): \( \left( \frac{3}{10} \right)^3 \)

Independent events greatly simplify probability calculations as they allow straightforward arithmetic when multiplying probabilities across multiple events.

Probability Calculations

Calculating probabilities is a fundamental aspect of understanding uncertainty and likelihood, especially with games of chance like a slot machine. The calculation process is fairly straightforward once you know the probabilities of single events and whether they are independent.

In our exercise, we assessed various probabilities:

• Three lemons: For each wheel, the probability of landing a lemon is \( \frac{3}{10} \). For three independent wheels, the combined probability is \( \left( \frac{3}{10} \right)^3 = \frac{27}{1000} \).
• No fruit symbols: Defining fruits as lemons or cherries, there's a \( \frac{5}{10} \) chance of spinning a non-fruit on one wheel. The chance for three wheels is \( \left( \frac{1}{2} \right)^3 = \frac{1}{8} \).
• Jackpot - 3 bells: Since the probability of a bell on one wheel is \( \frac{1}{10} \), the odds for all three wheels is \( \left( \frac{1}{10} \right)^3 = \frac{1}{1000} \).
• No bells: With a probability of \( \frac{9}{10} \) on one wheel, none showing bells is \( \left( \frac{9}{10} \right)^3 = \frac{729}{1000} \).

Understanding these calculations clarifies how different event probabilities are combined and manipulated to find outcomes on multiple independent components.