Question: Suppose that with the best technology one can measure nebulae distances with a standard deviation of 0.25 megaparsecs about their regression on recession velocity. Suppose further that one can observe nebulae whose recession velocities have a standard deviation of about 400 km/sec. How many nebulae should be sampled to obtain a 95% confidence interval on the age of the universe, with a width of 1 billion years? (Recall that 1 billion years is about 0.001021 megaparsec-seconds per kilometer.) How many nebulae are required if one can sample nebulae with recession velocities having a standard deviation of 600 km/sec?