Let's start with problem #1, which will give you a underlying knowledge for the other problems.

You have a number set of time scores as follows:

24, 18, 21, 17, 25, 19, 23, 17, 25, 15

To get standard deviation, you need variance, to get variance, you need mean. Go here, and enter your number set:

Mean, Variance, and Standard Deviation

Follow the math to see how to calculate mean, variance, and standard deviation.

Then we can move on to the other problems.