Lower and upper quartiles for a normal distribution?
X is a random variable that follows a normal distribution with a mean of 34 and a standard deviation of 5.
a) What proportion of X’s values lie between 30 and 40?
b) Find the lower and upper quartiles of X’s distribution.
Can someone check my answer for a) (please tell me where I went wrong, if it is incorrect):
= P(30-34/5) < Z < P(40-34/5)
= P(-.8) < Z < P(1.2)
= P(Z < 1.2) - P(Z < -.8)
= .8643 - .2119
And for b), I have no idea what to do, please help!