Most graphing calculators will do weighted averages pretty easily. It is mostly a matter of data entry.
mx = -2
my = 10
(x, y) = (mx, my)/10 = (-0.2, 1)
<span>The following choices may have a negative correlation: - speed of a car and minimum stopping distance - average running speed and total race time - outside temperature and amount of a heating bill
<span>Theses factors may yield negative results depending on the variables that will be present in a controlled experiment.</span></span>
a)
has CDF


where the last equality follows from independence of
. In terms of the distribution and density functions of
, this is

Then the density is obtained by differentiating with respect to
,

b)
can be computed in the same way; it has CDF


Differentiating gives the associated PDF,

Assuming
and
, we have


and


I wouldn't worry about evaluating this integral any further unless you know about the Bessel functions.