# Thread: What am I doing wrong with this normal probability distribution?

1. ## What am I doing wrong with this normal probability distribution?

Find z if the area to the left of z is 0.2981.

I subtract .5-.2981 and get .2019. When I look that up in the table, I get 0.53 but I was told that isn't right. I'm not sure what I am doing wrong.

2. I would consider $P(z<0.2981) = 1 - P(z>0.2981)$

3. OK, so when I do that this is what I come up with:

1-(0.5 - 0.2981) = 0.7981.

That doesn't look right to me because I can not find the value of z in the chart because the chart only goes up to 0.4999. I have no idea what I am doing here.

4. OK, it dawned on me that maybe 0.53 is actually correct but since it is to the left, it would be -0.53. Am I off base here or does that sound right to anyone?

5. Have a look at

Z table - Normal Distribution

Spoiler:
$P(z<0.2981) \approx 0.617187$

6. I used that calculator and came up with -0.5299, so I guess I was right with -0.53. Thanks for your help!