suppose that the probabilities of a customer purchasing 0, 1, or 2 books at a book store are , , and , respectively. what is the standard deviation of this customer's book purchases?

Iknow this isn't a question, but is there someway to ask a question under public safety or is there no category for it? i don't know if i'm overlooking it or not.

How many liters of 60% alcohol solution should be added to 40 liters of a 20% alcohol solution to make a 50% solution?

Which source would provide the most bias-free information about smoking and increased health risks? a) a website created by heart disease patients b) a research study conducted by the mayo clinic eliminate c) a public service message sponsored by tobacco companies d) an online question forum conducted by attorneys for cardiac specialists