I can't get these ones at all x.x please help

ABC College Bookstore sells Ti83 calculators. The random number of calculators sold per day along with the probabilities is:

# of calculators: 1, 2, 3, 4, 5

Probability: 1/8, 1/6, 1/2, 1/12, 1/8

What is the standard deviation for the number of calculators sold?

---

Find a 95% confidence interval for the mean weight of bass caught in El Capitan lake if a sample of 300 fish had a mean weight of 77 ozs. with a standard deviation of 12 ozs.

I've been trying to figure these out for a while and still can't get it right.