If the variance of a probability was computed to be 3.6 grams, what is the standard deviation?

Carlson Jewelers permits the return of their diamond wedding rings, provided the return occurs within two weeks of the purchase date. Their records reveal that 10 percent of the diamond wedding rings are returned. Five different customers buy five rings. What is the probability that none will be returned?

Sixty percent of the customers of a fast food chain order the Whopper, French fries and a drink. If a random sample of 15 cash register receipts is selected, what is the probability that 10 or more will show that the above three food items were ordered?

 If n = 100 and p= 1/5, determine the mean and standard deviation of this binomial distribution.

Judging from recent experience, 5 percent of the computer keyboards produced by an automatic, high-speed machine are defective. If six keyboards are randomly selected, what is the probability that none of the keyboards are defective?