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# Calculating mean and standard deviation in the given case

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A government agency has specialist who analyze the frequencies of letters of the alphabet in an attempt to decipher intercepted message. In standard English text, a particular letter is used at a rate of 5.9%

a. Find the mean and standard deviation for the number of times this letter will be found on a typical page of 1800 characters.

(Mean ?) = ________________
(Standard Deviation ?) = _____________

b. In an intercepted message, a page of 1800 characters is found to have the letter occurring 128 times. Is this unusual? Choose one below.

1. Yes, because 128 is below the minimum usual value.
2. Yes, because 128 is greater than the maximum usual value.
3. Yes, because 128 is within the range of usual values.
4. No, because 128 is within the range of usual values.

#### Solution Preview

a. Find the mean and standard deviation for the number of times this letter will be found on a typical page of 1800 characters.

Number of observations=n=1800
Probability of a particular letter=p=5.9%=0.059
q=1-p=1-0.059=0.941
Mean=np=1800*0.059=106.2
Standard ...

#### Solution Summary

The solution describes the steps to calculate mean and standard deviation in the given case.

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