Tom S. answered • 05/22/20

Highly Experienced, Patient High School, College, SAT/ACT Math Tutor

It would help if you submit some work on the problem. I will get you started.

In part 1, first find the missing probability for 20. What do the six probabilities in the table have to add up to? 1. So subtract 1 - the total of the other 5 probabilities to get the probability for 20. Then multiply each outcome times its probability and add all the products up to get the expected value.

In part 2, there are four steps to finding the standard deviation of random variables. First, calculate the expected mean time (done in part 1). Second, for each value in the group (0, 10, 20, 30, 40, 50) subtract the mean and multiply the result by the probability of that outcome occurring. Third, add the six results together. Fourth, find the square root of the result.

After you work on this, you may submit your work with further questions or to be checked.