# Thread: Normal Probability Distribution

1. ## Normal Probability Distribution

Suppose that a particular entrance examination into Public Service is designed so that the marks will be normally distributed with a mean of 300 and a standard deviation of 60. If only the top 15% of candidates are selected, what mark would a student be expected to obtain for admission?

I did .5 - .15 to find the percentage that would be below top 15% in the upper half.

=.35

went to my normal distribution table, found 3508 (closest listed to 3500) = 1.04 Z value.

Plugged 1.04 into z = (x - mean) / standard D

Z x S.D. + Mean = X

1.04 x 60 + 300 = 362.4

x = 362.4

Correct? Thanks in advance.

2. ## Re: Normal Probability Distribution

Originally Posted by Ploppies
Suppose that a particular entrance examination into Public Service is designed so that the marks will be normally distributed with a mean of 300 and a standard deviation of 60. If only the top 15% of candidates are selected, what mark would a student be expected to obtain for admission?

I did .5 - .15 to find the percentage that would be below top 15% in the upper half.

=.35

went to my normal distribution table, found 3508 (closest listed to 3500) = 1.04 Z value.

Plugged 1.04 into z = (x - mean) / standard D

Z x S.D. + Mean = X

1.04 x 60 + 300 = 362.4

x = 362.4

Correct? Thanks in advance.
More or less, yes.

CB