A sleep time of 15.9 hours per day for a newborn baby is at the 10th percentile of the distribution of sleep times for all newborn babies. Assuming the distribution is normal with standard deviation 0.5 hour, approximately what is the mean sleep time, in hours per day, for newborn babies?

Summary Submit Skip Question

The 10th percentile corresponds to a \(z\)-score of -1.28.

$$ z = \frac{x-\mu}{\sigma} $$ $$ -1.28 =\frac{15.9-\mu}{0.5} $$ $$ \mu = \boxed{-16.5} $$