Advanced Engineering Mathematics
Advanced Engineering Mathematics
10th Edition
ISBN: 9780470458365
Author: Erwin Kreyszig
Publisher: Wiley, John & Sons, Incorporated
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### Password Combinations and Probabilities

#### Problem Statement
A website requires users to create a 4-character long password. Each character can be a number, or a symbol chosen from ?, #, !, and $. The password does not have to include both numbers and symbols.

##### Questions:
a) How many 4-character passwords are possible if numbers and symbols can be used more than once?  
b) How many 4-character passwords are possible if no numbers or symbols can be repeated?  
c) What is the probability that a randomly generated 4-character password contains 4 different characters?

---

#### Solution:

---

**Part (a)**: Set up the expression that can be used to calculate the number of possible 4-character passwords if numbers and symbols can be used more than once.

- The expression is \[14^4\]. (Do not simplify.)  
   Here, 14 represents the total number of possible characters (10 digits + 4 symbols).

- The number of different passwords that are possible if numbers and symbols can be used more than once is \[38416\].

---

**Part (b)**: Determine the number of different passwords that are possible if no numbers or symbols can be repeated.

- Using the principle of permutation:  
 \[ 14 \times 13 \times 12 \times 11 \]

- Simplifying the expression:  
   \[ 24024 \]

---

**Part (c)**: Calculate the probability that a 4-character password contains 4 different characters.

- The probability is the number of favorable outcomes divided by the total number of outcomes.
- Probability = \[ \frac{24024}{38416} \approx 0.626 \]

In summary, the probability that a randomly generated 4-character password contains 4 different characters is approximately 0.626 (rounded to three decimal places).
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Transcribed Image Text:### Password Combinations and Probabilities #### Problem Statement A website requires users to create a 4-character long password. Each character can be a number, or a symbol chosen from ?, #, !, and $. The password does not have to include both numbers and symbols. ##### Questions: a) How many 4-character passwords are possible if numbers and symbols can be used more than once? b) How many 4-character passwords are possible if no numbers or symbols can be repeated? c) What is the probability that a randomly generated 4-character password contains 4 different characters? --- #### Solution: --- **Part (a)**: Set up the expression that can be used to calculate the number of possible 4-character passwords if numbers and symbols can be used more than once. - The expression is \[14^4\]. (Do not simplify.) Here, 14 represents the total number of possible characters (10 digits + 4 symbols). - The number of different passwords that are possible if numbers and symbols can be used more than once is \[38416\]. --- **Part (b)**: Determine the number of different passwords that are possible if no numbers or symbols can be repeated. - Using the principle of permutation: \[ 14 \times 13 \times 12 \times 11 \] - Simplifying the expression: \[ 24024 \] --- **Part (c)**: Calculate the probability that a 4-character password contains 4 different characters. - The probability is the number of favorable outcomes divided by the total number of outcomes. - Probability = \[ \frac{24024}{38416} \approx 0.626 \] In summary, the probability that a randomly generated 4-character password contains 4 different characters is approximately 0.626 (rounded to three decimal places).
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