15. Deciphering Messages The Central Intelligence Agency has specialists who analyze the frequencies of letters of the alphabet in an attempt to decipher intercepted messages.

In standard English text, the letter r is used at a rate of 7.7%.

a. Find the mean and standard deviation for the number of times the letter r will be found on a typical page of 2600 characters.

b. In an intercepted message sent to Iraq, a page of 2600 characters is found to have the letter r occurring 175 times. Is this unusual?