Four siblings are 2, 6, 9, and 10 years old.

a. Calculate the mean of their current ages. Round to the nearest tenth.

b. Without doing any calculation, predict the mean of their ages 10 years from now. Check your prediction by calculating their mean age in 10 years (when they are 12, 16, 19, and 20 years old).

c. Calculate the standard deviation of their current ages. Round to the nearest tenth. 

d. Without doing any calculation, predict the standard deviation of their ages 10 years from now. Check your prediction by calculating the standard deviation of their ages in 10 years.

e. Adding 10 years to each of the siblings ages had different effects on the mean and the standard deviation. Why did one of these values change while the other remained unchanged? How does adding the same value to each number in a data set affect the mean and standard deviation?