.-. I need your help .-.

What is the standard deviation of the following data set rounded to the nearest tenth? 3, 17, 18, 15, 12, 21, 9

The height of a flare fired from the deck of a ship in distress can be modeled by h(t)= -2(8t^2-52t-28), where h is the height of the flare above water and t is the time in seconds. a. find the time it takes the flare to hit the water.

Which of the following is an irrational number