# Math Help - Zscore/Standard Normal Probabilities

1. ## Zscore/Standard Normal Probabilities

Given:
mu = 65.7
sigma = 15
Standard normal distribution

Question:
20% of the area will be less than what x value?

I looked at my z-score table and couldn't find .0200 so now I have no clue how to even begin!

2. From your z-score table $P(z< -0.8416)= .2$

Use this fact in $z = \frac{x-\mu}{\sigma} \implies -0.8416 = \frac{x-65.7}{15}$ to solve for $x$

3. Where did you get .8416? Could you possibly have a more complete z-score table or am I missing some intermediary calculation?

4. Originally Posted by tom ato
Where did you get .8416? Could you possibly have a more complete z-score table or am I missing some intermediary calculation?
You could just as easily use -0.84. There is no missing step here, and you no doubt are meant to use -0.84.