how to use standard deviation, I don't really understand how to calculate and use the formula, someone can please give me an example with formula it would be great thank you so much. 

You would like to purchase one class a share of berkshire hathaway through your scottrade brokerage account. scottrade charges a ​$6 commission for online trades. you log into your​ account, check the​ real-time quotes for berkshire hathaway​ (you see a bid price of ​$262 comma 900 and an ask price of ​$263 comma 730​) and submit your order. a. what is the current​ bid/ask spread for berkshire hathaway class a​ shares? b. if scottrade routes your buy order to the​ nyse, where berkshire hathaway is​ listed, what's the potential minimum your total transaction costs will​ be? c.​ if, instead, scottrade routes your buy order to​ nasdaq, where berkshire hathaway is not​ listed, what's the potential maximum your total transaction costs will​ be? d. regardless of how your trade is​ executed, based on the​ bid/ask spread, what is the market value of your​ trade? a. the current​ bid/ask spread for berkshire hathaway class a shares is ​$ nothing. ​(round to the nearest​ dollar.)