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Box of chocolates According to Forrest Gump, "Life is like a box of chocolates. You never know what you're gonna get." Suppose a candy maker offers a special "Gump box" with 20 chocolate candies that look the same. In fact, 14 of the candies have soft centers and 6 have hard centers. Choose 2 of the candies from a Gump box at random.(a) Draw a tree diagram that shows the sample space of this chance process. (b) Find the probability that one of the chocolates has a soft center and the other one doesn't.

Short Answer

Expert verified
The probability of selecting one soft and one hard chocolate is \( \frac{42}{95} \).

Step by step solution

01

Understand the Sample Space

The Gump box contains 20 chocolates: 14 with soft centers and 6 with hard centers. When selecting 2 candies from the box, various combinations are possible. We need to explore these using a tree diagram to understand all potential outcomes.
02

Drawing the Tree Diagram

Begin the tree diagram with a first choice leading to two branches: one for choosing a soft and the other for a hard chocolate. From each of these branches, add two more branches representing a second selection. This results in four endpoint branches corresponding to four outcomes: soft-soft, soft-hard, hard-soft, and hard-hard.
03

Determining Outcome Probabilities

The probability of each branch or outcome can be found by calculating the probabilities as follows: - Probability of soft-soft: \( \frac{14}{20} \cdot \frac{13}{19} = \frac{182}{380} \)- Probability of soft-hard: \( \frac{14}{20} \cdot \frac{6}{19} = \frac{84}{380} \)- Probability of hard-soft: \( \frac{6}{20} \cdot \frac{14}{19} = \frac{84}{380} \)- Probability of hard-hard: \( \frac{6}{20} \cdot \frac{5}{19} = \frac{30}{380} \).Ensure the sum of probabilities equals 1 as a sanity check.
04

Calculating Required Probability

To find the probability of selecting one soft and one hard chocolate, combined probabilities of the soft-hard and hard-soft outcomes since order does not matter: \( \frac{84}{380} + \frac{84}{380} = \frac{168}{380} \). Simplifying this fraction gives \( \frac{84}{190} \) or further to \( \frac{42}{95} \).

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Key Concepts

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

Sample Space
The sample space in probability is the set of all possible outcomes. For our box of chocolates, the sample space reflects the different combinations of candies we can select. We have 20 chocolates with 14 soft and 6 hard centers. When we choose two chocolates, every pair represents an item in our sample space.

The combinations for two chocolates from the Gump box include:
  • Soft-Soft: Both chocolates have soft centers.
  • Soft-Hard: One chocolate has a soft center, the other a hard center.
  • Hard-Soft: First chocolate has a hard center, second one soft.
  • Hard-Hard: Both chocolates have hard centers.
By listing all these possibilities, we have effectively created our sample space. In probability problems, understanding the sample space is crucial as it forms the foundation for calculating probabilities.
Tree Diagram
A tree diagram is a visual representation of all possible outcomes in a probability scenario. It helps organize complex probability problems by breaking them down into a series of sequential random choices.

For the Gump box exercise:
  • Start with a single point, which represents the box before any candy is selected.
  • The first level of branches represents the two choices for the first candy: soft or hard.
  • Each branch then splits again for the second choice, showcasing all possible sequences of choices.
The resulting diagram aids in visualizing all scenarios like soft-soft, soft-hard, hard-soft, and hard-hard. Each path through the tree represents a distinct outcome, making complex selections simpler to manage.
Combinatorial Probability
Combinatorial probability involves calculating the likelihood of various outcomes by counting combinations and arrangements of events. For our chocolates, we calculate the probability of each event based on combinations of soft and hard-centered candies.

Each probability is derived by multiplying the fraction of choosing each candy at each step of the selection. For example:
  • Soft-Soft: First is soft, and second is soft, \[\frac{14}{20} \times \frac{13}{19} = \frac{182}{380}.\]
  • Soft-Hard: First is soft, and second is hard, \[\frac{14}{20} \times \frac{6}{19} = \frac{84}{380}.\]
  • Hard-Soft: First is hard, and second is soft, \[\frac{6}{20} \times \frac{14}{19} = \frac{84}{380}.\]
  • Hard-Hard: First is hard, and second is hard, \[\frac{6}{20} \times \frac{5}{19} = \frac{30}{380}.\]
This approach lets us see the proportion of each event relative to all possible selections.
Conditional Probability
Conditional probability is about finding the probability of an event given that another event has already occurred. In the chocolate box problem, after choosing the first candy, the available combinations for the second choice adjust based on this first selection.

Consider calculating probabilities for mixed selection:
  • The probability of one soft and one hard chocolate is the sum of the soft-hard and hard-soft paths in the tree: \[\frac{84}{380} + \frac{84}{380} = \frac{168}{380}.\]
  • This fraction simplifies to \[\frac{42}{95}.\]
Conditional probability helps answer questions about these dependent outcomes by focusing on what's left in the sample space after one event occurs.

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Most popular questions from this chapter

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