Statistics: Probability Help Needed

Question

A publisher prints 300 words per page in its books. Historically the publisher has found that authors make, on average, one typo every 250 words:

1.How many typos would you expect to find in single page?

2.What is the probability that there are exactly two typos in the page?

3.What is the probability that there is at least one typo in a page?

Answer 1

Jess, The probability of any single word having a typo would be p = 1/250.

 

We can consider each word's correctness to be independent of any other making this a binomial distribution with n=300.

 

Then the formulas and techniques of a binomial would apply here.

 

In particular e.g.

 

1. Expected value of the distribution would be np=300/250. This is the mathematical expectation. Since it is not a whole number you might be expected to round it off to one.

 

For parts 2 and 3 try using the formula for binomial probabilities.

 

 

Let me know if you understand it.

Arnold