111k views
2 votes
The Central Intelligence Agency (CIA) has specialists who analyze the frequencies of letters of the alphabet in an attempt to decipher intercepted messages. In standard English text, the letter n is used at a rate of 6.65%. Find the mean and standard deviation for the number of times the letter n will be found on atypical page of 2300 characters.

User Gorka
by
7.7k points

1 Answer

2 votes

Final answer:

To find the mean number of times 'n' appears on a page, multiply the number of characters (2300) by the frequency (6.65%), resulting in approximately 153 'n's per page. The standard deviation is found using the square root of 2300 multiplied by the probability of 'n' and its complement, resulting in approximately 12.197.

Step-by-step explanation:

The student is asking a question related to the use of probability and statistics to analyze frequencies of letters in English text, specifically focusing on the letter 'n'. Given that 'n' appears in standard English text at a rate of 6.65%, and considering a typical page to consist of 2300 characters, we wish to find the mean and standard deviation for the occurrence of 'n' on such a page. Using the binomial distribution assumptions, where n is the number of trials (characters on a page) and p is the probability of success (the letter 'n' appearing), the mean (expected value) is calculated as:

Mean (μ) = n * p

Substitute the given values:

μ = 2300 * 6.65% ≈ 153.045

This means on average, we expect to see about 153 instances of the letter 'n' on a page. To find the standard deviation (σ), we use the formula for the binomial distribution:

Standard Deviation (σ) = √(n * p * (1 - p))

Substitute the given values:

σ = √(2300 * 0.0665 * (1 - 0.0665)) ≈ √(153.045 * 0.9335) ≈ 12.197

Thus, the standard deviation is approximately 12.197, indicating the variability we might expect in the count of 'n's on a page.

User Arphile
by
7.3k points