For the past several years, the Philadelphia Fire Departments has been keeping track of the number of fire hydrants that been opened illegally daily during heat waves. These data(rounded to the nearest 10) are given in the table below. Use the information to calculate how many hydrants the department should expect to be opened per day during the upcoming heat wave also find the Standard deviation of number of fire hydrants opened. [6 points]

Hydrantsopened 20 30 40 50 60 70

Days 14 12 15 11 9 1