An oak tree that is 220 years old produced acorns at two different rates. until it reached maturity, it produced an average of 900 acorns a year. however, once the tree reached maturity, it produced an average of 2200 acorns a year. one particular tree, angel oak, has produced about 289,000 acorns in its lifetime. at what age did it reach maturity?
a) 188
b) 150
c) 138
d) 148

Afactory makes propeller drive shafts for ships. a quality assurance engineer at the factory needs to estimate the true mean length of the shafts. she randomly selects four drive shafts made at the factory, measures their lengths, and finds their sample mean to be 1000 mm. the lengths are known to follow a normal distribution whose standard deviation is 2 mm. calculate a 95% confidence interval for the true mean length of the shafts. input your answers for the margin of error, lower bound, and upper bound.