Probability of ACT Scores

In recent years, the ACT scores for high school students with 3.5 to 4.0 GPA were normally distributed, with a mean of 24.3 and a standard deviation of 4.2. If one of the students is randomly selected, find the probability that the students ACT score is between 20 and 29.

I have done the problem, and everytime I put in the answer it is telling me that it is too low. This is the work that I have done on it so far. Any suggestions would be greatly appreciated.

(20-24.3)/4.2=-.956 which rounds to -.96, and the z score would be .1685

(29-24.3)/4.2=1.119 which rounds to 1.12, and the z score would be .8686

Then, I subtracted .1685 from .8686 and came up with an answer of .7001.

Once again, thank you in advance for any advice that can be given.

camcascod said:

I have done the problem, and everytime I put in the answer it is telling me that it is too low.

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What do you mean when you say that "it is telling me"? What is "it"?

Also, I'm not sure if the reply here might be helpful...?

Thank you.

Eliz.

The "it" is where our teacher has us put our answers in to make sure we are getting the right answers. The reply really didn't help, because I have to find the sd and it is already given in that problem.

camcascod said:

The "it" is where our teacher has us put our answers in to make sure we are getting the right answers.

Click to expand...

So you're writing down your answers on your paper, and the answer sheet is talking back...?

camcascod said:

The reply really didn't help, because I have to find the sd and it is already given in that problem.

Click to expand...

I will guess that "sd" means "standard deviation", but isn't that given in your exercise as being 4.2...?

The only difference I could see between your exercise and the other was that some specific values were different. Both are related to the ACT, to the scores, with a given standard deviation and mean, and you're asked for the probability that a given random student will have a score within a certain range. How is your question qualitatively different?

Please be specific. Thank you.

Eliz.

Response

The teacher has a website set up where we can put in the answer we came up with, so we know that we are on the right track.

I am sorry, sd does stand for standard deviation.

I will look at the problem again, and hopefully it can help me.

I figured it out!

Thank you for the pointers, I figured out how to do the problem.