Question 1048251
mean of 71 mph and a standard deviation of 8 mph. 
{{{z =blue (x - mu)/blue(sigma)}}}
a. P(x<= 65) = P(z <=  -6/8) =  P(z <=  -3/4)
TI syntax is normalcdf(smaller z, larger z) 
normalcdf( ... is a command people using a TI Calculator
use for finding the area under a standard normal curve
between two z=values...-9999 used for the far far left z-value
to give us what we want: area under a standard normal curve for
a particular z-value, in this case z = -.75 (Area under the curve to left of Blue Line)
normalcdf(-9999, -.75) = .2266  0r 22.66%
{{{drawing(400,200,-5,5,-.5,1.5, graph(400,200,-5,5,-.5,1.5, 0,exp(-x^2/2)), blue(line( -.75,0, -.75,exp(-.75^2/2))),locate(4.8,-.01,z),locate(4.8,.2,z),locate(.4,-.02,z))}}}

b . P(x<= 50) = P(z <=  -21/8)
normalcdf(-9999, -21/8) = .0043  0r .43%
One can use table as well to find the z-value