# Math Help - Standard normal distribution

1. ## can any one help me out!!! -the answer still not right!!

If Z is a random variable having the standard normal distribution,find

A) P (Z>=-0.79);
B) P (-1.90>=Z>=0.44).

2. Hello,
Originally Posted by Yan
If Z is a random variable having the standard normal distribution, find
A) P (Z>=-0.79);
B) P (-1.90>=Z>=0.44).
Here are general rules for the standard normal distribution (and it will look very logical if you look at a z-table : http://www.science.mcmaster.ca/psych...e/z-table2.jpg)

define p(.) as the black area. it's defined for positive values.

If a>0
P(Z>a)=0.5-p(a)
P(Z<a)=1-P(Z>a)=0.5+p(a)

If a<0
P(Z<a)=P(Z>-a)=0.5-p(-a)
P(Z>a)=P(Z<-a)=0.5+p(-a)

P(a<Z<b)=P(Z<b)-P(Z<a)

and that's all ^^

3. Originally Posted by Moo
Hello,

Here are general rules for the standard normal distribution (and it will look very logical if you look at a z-table : http://www.science.mcmaster.ca/psych...e/z-table2.jpg)

define p(.) as the black area. it's defined for positive values.

If a>0
P(Z>a)=0.5-p(a)
P(Z<a)=1-P(Z>a)=0.5+p(a)

If a<0
P(Z<a)=P(Z>-a)=0.5-p(-a)
P(Z>a)=P(Z<-a)=0.5+p(-a)

P(a<Z<b)=P(Z<b)-P(Z<a)

and that's all ^^
but i still don't know how to do the (b) part?

4. Originally Posted by Yan
but i still don't know how to do the (b) part?
0, since -1.9 can't be > 0.44

5. Originally Posted by Moo
0, since -1.9 can't be > 0.44
but, in my solution sheet, the answer is 0.6134

$P(-1.90\le Z \le 0.44)$.