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1 is 0.8. If you get contract \(\\# 1,\) the probability you also get contract \(\\# 2\) wil… # Your company bids for two contracts. You believe the probability you get contract #1 is 0.8. If you get contract \(\\# 1,\) the probability you also get contract \(\\# 2\) will be \(0.2,\) and if you do not get \(\\# 1,\) the probability you get #2 will be 0.3. a) Are the two contracts independent? Explain. b) Find the probability you get both contracts. c) Find the probability you get no contract. d) Let \(X\) be the number of contracts you get. Find the probability model for \(X\) e) Find the expected value and standard deviation.

Short Answer

Expert verified
a) No, they are not independent. b) 0.16 c) 0.14 d) X=0 (0.14), X=1 (0.58), X=2 (0.16) e) E(X)=0.86, \(\sigma\approx 0.651\).

Step by step solution

01

Define Independence

Two events A and B are independent if the probability of both events happening is equal to the product of their individual probabilities. Formally, events A and B are independent if \( P(A \cap B) = P(A) \cdot P(B) \). In this context, we need to check if this holds for contracts #1 and #2.
02

Calculate Individual Probabilities

We know \( P( ext{Contract #1}) = 0.8 \). If contract #1 is obtained, \( P( ext{Contract #2 | Contract #1}) = 0.2 \) and if not, \( P( ext{Contract #2 | Not Contract #1}) = 0.3 \).
03

Are Contracts Independent?

To determine independence we need to check if \( P( ext{Contract #2}) = P( ext{Contract #2 | Contract #1}) \). Since \( 0.2 eq 0.3 \), the contracts are not independent.
04

Calculate Probability of Both Contracts

The probability of getting both contracts is \( P( ext{Contract #1}) \cdot P( ext{Contract #2 | Contract #1}) = 0.8 \times 0.2 = 0.16 \).
05

Calculate Probability of No Contracts

The probability of not getting either contract is \( P( ext{Not Contract #1}) \cdot P( ext{Not Contract #2 | Not Contract #1}) = (1-0.8) \times (1-0.3) = 0.2 \times 0.7 = 0.14 \).
06

Find Probability Model for X

Let \( X \) be the number of contracts obtained. The possible values for \( X \) are 0, 1, or 2. \( P(X=0) \) is the probability of getting no contracts, \( P(X=1) \) combines the probabilities of getting exactly one contract, and \( P(X=2) \) is the probability of getting both contracts.
07

Calculate Probabilities for X=0, X=1, X=2

\( P(X=0) = 0.14 \), \( P(X=1) = \) (getting only contract #1 or only contract #2). For only contract #1, \( 0.8 \times 0.8 = 0.64 \); for only contract #2, \( 0.2 \times 0.3 = 0.06 \). Hence, \( P(X=1) = 0.58 \). \( P(X=2) = 0.16 \) from step 4.
08

Calculate Expected Value and Standard Deviation

Expected value \( E[X] \) is found by summing \( x_i \cdot P(X=x_i) \) for each outcome \( x_i \). Calculate this as \( 0 \times 0.14 + 1 \times 0.58 + 2 \times 0.16 = 0.86 \). Compute variance \( \sigma^2 = \sum (x_i - E[X])^2 \cdot P(X=x_i) \) yielding \( \sigma^2 = 0.4248 \), so \( \sigma = \sqrt{0.4248} \approx 0.651 \).

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Key Concepts

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

Independent Events
In probability theory, two events are considered independent if the occurrence of one event does not influence the occurrence of the other. To mathematically determine independence, we use the formula: \[ P(A \cap B) = P(A) \cdot P(B) \]Here, \(P(A \cap B)\) is the probability that both events \(A\) and \(B\) occur at the same time. If this equation holds true, then the events are independent.In the context of the exercise, we are evaluating two contract bids. If obtaining contract \#1 affects the probability of obtaining contract \#2, then these events are not independent. According to the problem, the probability of getting contract \#2 changes based on whether contract \#1 is obtained or not, hence indicating dependency between the two events.
Expected Value
The expected value is a fundamental concept in probability, representing the average outcome one could expect from a random process over the long run. For discrete random variables, like the number of contracts obtained in this exercise, the expected value \(E[X]\) can be calculated using:\[ E[X] = \sum (x_i \cdot P(X=x_i)) \]Where \(x_i\) are the possible outcomes, and \(P(X=x_i)\) are their respective probabilities.In this example, the possible outcomes are getting 0, 1, or 2 contracts. The expected value is determined by multiplying each outcome by its probability and summing the results. This gives us insights into the "average" number of contracts we might receive if the bidding process were repeated many times.
Standard Deviation
Standard deviation, in probability, measures the amount of variation or dispersion of a set of values. It's based on the variance, which is the average of the squared differences from the Mean. For a probability distribution, it provides insights into how much the outcomes vary from the expected value.To find the standard deviation:1. Calculate the expected value \(E[X]\).2. Compute the variance \(\sigma^2\) using:\[ \sigma^2 = \sum (x_i - E[X])^2 \cdot P(X=x_i) \]3. The standard deviation \(\sigma\) is the square root of the variance:\[ \sigma = \sqrt{\sigma^2} \]In the exercise, this measure differs with each possible outcome of contracts, highlighting how spread out these probabilities are around the expected value.
Probability Model
A probability model provides a mathematical description of a random experiment's possible outcomes and their likelihoods. In the context of the contracts exercise, a probability model helps us understand the probabilities of receiving different numbers of contracts.For example, let \(X\) denote the number of contracts acquired. The probability model lists the possible values of \(X\) (0, 1, or 2 contracts) along with the associated probabilities. These probabilities can be calculated using:- \(P(X=0)\): Probability of getting no contracts.- \(P(X=1)\): Probability of getting exactly one contract.- \(P(X=2)\): Probability of getting both contracts.This model provides a clear framework for anticipating the outcomes of the bid processes, helping in making strategic decisions based on the likelihood of each scenario.

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