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In a test of a printed circuit board using a random test pattern, an array of 10 bits is equally likely to be 0 or 1 . Assume the bits are independent. (a) What is the probability that all bits are \(1 \mathrm{~s} ?\) (b) What is the probability that all bits are 0 s? (c) What is the probability that exactly five bits are \(1 \mathrm{~s}\) and five bits are 0 s?

Short Answer

Expert verified
(a) \( \frac{1}{1024} \), (b) \( \frac{1}{1024} \), (c) \( \frac{63}{256} \).

Step by step solution

01

Understanding the Scenario

We have a 10-bit random test pattern where each bit is equally likely to be 0 or 1, and the bits are independent of each other. This means each bit has a probability of 0.5 of being 1 and 0.5 of being 0. We are asked to calculate probabilities for certain patterns in this array.
02

Calculating Probability of All Bits Being 1s

Since each bit is independent and the probability of one bit being 1 is 0.5, the probability of all 10 bits being 1 is \( (0.5)^{10} \). Multiply 0.5 by itself 10 times:\[ P( ext{All bits are } 1) = (0.5)^{10} = \frac{1}{1024} \]
03

Calculating Probability of All Bits Being 0s

This is similar to calculating the probability of all bits being 1s. The probability of one bit being 0 is also 0.5, so the probability that all 10 bits are 0 is \( (0.5)^{10} \).\[ P( ext{All bits are } 0) = (0.5)^{10} = \frac{1}{1024} \]
04

Calculating Probability of Exactly Five 1s and Five 0s

To find this, we use the binomial probability formula: \( P(X=k) = \binom{n}{k} p^k (1-p)^{n-k} \), where \( n = 10 \) is the total number of trials, \( k = 5 \) is the desired number of successes (1s), and \( p = 0.5 \) is the probability of success in each trial. First, calculate the binomial coefficient \( \binom{10}{5} \), which represents the number of ways to choose 5 bits as 1s out of 10:\[ \binom{10}{5} = \frac{10!}{5!5!} = 252 \]Now calculate the full probability:\[ P( ext{Exactly 5 bits are } 1) = 252 imes (0.5)^5 imes (0.5)^5 = 252 imes \left(\frac{1}{32}\right) imes \left(\frac{1}{32}\right) = \frac{252}{1024} = \frac{63}{256} \]

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Key Concepts

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

Binomial Probability
Binomial probability is a critical concept in probability theory that helps describe the likelihood of certain outcomes when there are two possible results, like a coin flip resulting in heads or tails. Imagine conducting a series of experiments where each experiment has two possible outcomes: success or failure. The binomial probability model is perfect for predicting results from such experiments. For example, when considering the probability of getting exactly five 1s when flipping bits, the binomial probability formula comes in handy.
  • It uses parameters: number of trials (), number of successes desired (), probability of success in each trial ().
  • The formula is: \[ P(X=k) = \binom{n}{k} \cdot p^k \cdot (1-p)^{n-k} \]
  • This is because each bit has a chance of being 1 (success) or 0 (failure) each trial.
This formula provides a comprehensive approach for calculating probabilities over multiple trials, useful for situations where independent outcomes follow a dichotomous distribution.
Independent Events
Independent events are a fundamental idea in probability theory, essential for understanding how probabilities work in scenarios like our bit array. When two events are independent, the occurrence of one does not affect the probability of the other. This concept is crucial for the test pattern of bits because each bit's value does not influence any others. This independence allows us to simplify the problem:
  • The probability of any single event, such as a bit being 1 or 0, is unaffected by other bits' outcomes.
  • This property leads to easier calculations for multiple trials, as you can multiply the probabilities of individual events to find joint probabilities.
For instance, calculating the probability of all bits being set to 1 relies on multiplying each bit being 1: \[ P(\text{All bits are } 1) = (0.5)^{10} \]This method highlights the simplicity that comes with independent events when dealing with probabilities.
Random Variables
Random variables are a cornerstone of probability theory, representing quantities whose outcomes depend on chance. They offer a way to quantify uncertainty in probability experiments, linking real-world phenomena to mathematical frameworks. In our test pattern scenario, each bit's outcome (0 or 1) can be modeled as a random variable X where:
  • X can take values 0 or 1, representing each outcome.
  • The probability distribution of X describes the likelihood of these outcomes.
  • For a single bit, X is a Bernoulli random variable
When considering ten such bits, we deal with multiple independent random variables that together form a binomial distribution. Calculations such as finding exactly five bits being 1 rely on viewing the sum of such independent random variables, transforming complex scenarios into manageable mathematical equations.
Random variables allow us to predict and analyze systems with inherent randomness effectively, crucial for understanding outcomes in any probability-based scenario.

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Most popular questions from this chapter

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