# Probabilities

1. Letter and Digit. A new computer owner creates a password consisting of two characters. She randomly selects a letter of the alphabet for the first character and a digit (0,1,2,3,4,5,6,7,8,9) for the second character. What is the probability that her password is "k9"? Would this password be effective as a deterrent against someone trying to gain access to her computer?

2. Poll Confidence level. It is common for public opinion polls to have a "confidence level" of 95%, meaning that there is a 0.95 probability that the poll results are accurate within the claimed margins of error. If five different organizations conduct independent polls, what is the probability that all five of them are accurate within the claimed margins of error? Does the result suggest that with a confidence level of 95%, we can expect that almost all polls will be within the claimed margin error? 0.956

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1. Letter and Digit. A new computer owner creates a password consisting of two characters. She randomly selects a letter of the alphabet for the first character and a digit (0,1,2,3,4,5,6,7,8,9) for the second character. What is the probability that her password is "k9"? Would this password be effective as a deterrent against someone trying to gain access to her computer?

There are 26 letters of the alphabet so the probability of selecting any particular letter is .

There are 10 possible digits so the probability of ...

#### Solution Summary

This provides two examples of probability, one with letter and digit combinations, and one with poll confidence level.