The frequency distribution presented describes the speed at which some young people drove to get to take their classes at the university. These young people were driving on a road with a speed limit of 35 mi / h. Find the variance and standard deviation. Speed frecuency 42-45 25 46-49 16 50-53 8 54-57 4 58-61 2

I need help finding the standard deviation.

Four students take tests.  The results of each test for the class and the student are listed in the choice.  Which student has the highest Z Score? a.John who scored an 85 and whose class averages 77 with a standard deviation of 4. b.Tammy who scored an 86 and whose class averages 82 with a standard deviation of 3. c.Rob who scored an 87 and whose class averages 73 with a standard deviation of 11. d.Sandra who scored a 90 and whose class averaged an 81 with a standard deviation of 7.

The ages​ (in years) of a random sample of shoppers at a gaming store are shown. Determine the​ range, mean,​ variance, and standard deviation of the sample data set. 12, 20, 23, 13, 18, 17, 22, 17, 15, 16 The range is The mean is ( Simplify your answer. Round to the nearest tenth as​ needed.) The variance is (Simplify your answer. Round to the nearest hundredth as​ needed.) The standard deviation is (Simplify your answer. Round to the nearest tenth as​ needed.) Can you please explain me this math problem having trouble understanding. Thank you.