:11. A study of 500 babies looked at the relationship between
their weight at birth and the age at which they first slept
through the night.  The birth weights of the babies averaged out
to 90 ounces, with an SD of 15 ounces. The ages at which they
first slept through the night average 50 days with an SD of 10
days.  The correlation between the two variables was -0.60.
Consider the babies who weighed 105 ounces at birth.  The
percentage of them who first slept through the night at an age of
50 days or earlier is closest to <p>

a.  35%
 b.  50%
 c.  60%
 d.  75%
 e.  99% <p>

(Assume that the scatter diagram is football-shaped and
homoscedastic)