# Just need a little help??

#### MicheleC82

##### New Member
Okay I am really bad at this stuff so if I could get some help on this problem??

Your chemistry instructor informs you that she will grade your final exam on a curve. You discover he will give an A to those who scored in the top 10% of the class . Those who score above the bottom 70% abd below the top 10% will recieve a B. Those who score above the bottom 30% and below the top 30% will recieve a C. Suppose you must gt a C or better on the final exam to pass the course.THe test scores are normally distributed with a mean of 25 and a standard deviation of 5 . What is the minimum score you must recieve on the final exam to pass the course? If you earned a score of 29 what is your final grade on the exam?

If I could just get an example of how to do this one that would be great cause I have a bunch of problems to do like this

#### JohnM

##### TS Contributor
This uses the standard normal distribution. You are given the percentile ranges for each letter grade. Convert the percentile ranges into z scores (look up in the normal distribution table) and then convert the z scores into raw scores using a mean of 25 and std dev of 5.

In order to get a C, you need to be above the bottom 30% of the area under the curve. Find the z score corresponding to the point dividing the bottom 30% from the top 70%. Then use the formula z = (x - mu)/s to find x, which is the score you need to pass.

A raw score of 29 equals a z score of:
z = (29-25)/5 = 0.8

Convert the z score into a percentile to figure out the corresponding letter grade.

#### MicheleC82

##### New Member
JohnM said:
This uses the standard normal distribution. You are given the percentile ranges for each letter grade. Convert the percentile ranges into z scores (look up in the normal distribution table) and then convert the z scores into raw scores using a mean of 25 and std dev of 5.

In order to get a C, you need to be above the bottom 30% of the area under the curve. Find the z score corresponding to the point dividing the bottom 30% from the top 70%. Then use the formula z = (x - mu)/s to find x, which is the score you need to pass.

A raw score of 29 equals a z score of:
z = (29-25)/5 = 0.8

Convert the z score into a percentile to figure out the corresponding letter grade.

THank you soooo much, this really helps!!!!!!

Michele