Math Help - Z-Scores.. tell me if im right please!

1. Z-Scores.. not sure how to figure this one out

Will post what I got when I get something!.. heh dont let me not having an answer stop you ;/
For the second one i got aprox .39% of the population.
got 40 for the first one

For the second one i think it is 12 and 0 respectively, not sure how to calculate the third one. got 69 for C

2. Solution for question 6

to figure out the z score use this formula:

$
z = \frac{score - average}{standard deviation}
$

mean = 50 sd = 10 and z = 1

$
1 = \frac{x - 50}{10}
$

10 = x - 50

x = 60

3. What does it mean z-score and how does it work?

4. Originally Posted by ThePerfectHacker
What does it mean z-score and how does it work?
z score is the result of transforming a RV $X\sim N(\mu,\sigma^2)$ by letting:

$z=\frac{x-\mu}{\sigma}$.

Then $Z\sim N(0,1)$.

In rough terms it is the transform that is applied to allow the use of tables
of the standard normal distribution to be used to obtain probabilities for
random variables which have a normal distribution which is not standard.

RonL