Question: The attention span of a two year old is exponentially distributed with a mean of about 8 minutes. Suppose we randomly survey 60 two year-olds.

a. In words, X =

b. X ~

c. In words, ? ?X

d. ?X ~

e. Before doing any calculations, which do you think will be higher:

i. the probability that an individual attention span is less than 10 minutes or ii. the probability that the average attention span for the 60 children is less than 10 minutes?

Why?

f. calculate the probabilities in part (e).

g. explain why the distribution for ?X is not exponential.