# Thread: Expected Difference and Other Stuff (ACT scores for 1,171,460 members of class)

1. ## Expected Difference and Other Stuff (ACT scores for 1,171,460 members of class)

ACT scores for the 1,171,460 members of the 2004 members high school graduating class who took the test closely followed the Normal Distribution with mean 20.9 and standard deviation 4.8. Choose two students independently and at random from this group.

a) What is the expected difference in their scores?
b) What is the standard deviation of the difference in their scores?
c) Find the probability that the difference in the two students' scores is greater than 6.

Thanks for all of your help!!!!

2. Originally Posted by jalyn757
ACT scores for the 1,171,460 members of the 2004 members high school graduating class who took the test closely followed the Normal Distribution with mean 20.9 and standard deviation 4.8. Choose two students independently and at random from this group.

a) What is the expected difference in their scores?
b) What is the standard deviation of the difference in their scores?
c) Find the probability that the difference in the two students' scores is greater than 6.

Thanks for all of your help!!!!

Please share your work with us ...even if you know it is wrong.

If you are stuck at the beginning tell us and we'll start with the definitions.

http://www.freemathhelp.com/forum/announcement.php?f=33

3. Originally Posted by Subhotosh Khan

Please share your work with us ...even if you know it is wrong.

If you are stuck at the beginning tell us and we'll start with the definitions.

http://www.freemathhelp.com/forum/announcement.php?f=33

So I am stuck with what it is asking and I don't even know where to begin!

4. I just don't know where to start! I am having trouble understanding how to find what its asking or even to understand what I'm trying to find

5. Originally Posted by jalyn757
ACT scores for the 1,171,460 members of the 2004 members high school graduating class who took the test closely followed the Normal Distribution with mean 20.9 and standard deviation 4.8. Choose two students independently and at random from this group.

a) What is the expected difference in their scores?
b) What is the standard deviation of the difference in their scores?
c) Find the probability that the difference in the two students' scores is greater than 6.
In order to help you most effectively, we need to know what you DO know, so we have a place to start. What have you been learning that might be useful in answering this? Presumably you know something about random variables and probability distributions, and about the normal distribution in particular. Here we have two random numbers from the same normal distribution; what do you know about the distribution of their difference?

Also, be sure to proofread the question. I think, at the least, you put in the word "members" an extra time (unless the author or publisher of the problem did that).