Help with Prob and Stat question

[orangeb]

I received a homework assignment back that was wrong and I'm not sure how to do the problem. The teacher is ignoring my questions on it. Can someone help? The question is:
Find the sample size, sample mean, midrange, range, average deviation, sample variance and standard deviation for the following sample data: 60,90,80,70,50. I had 5 for the sample size which was correct, 70 for the Sample mean, 20 for the midrange 40 for the Range 5 for the Average deviation 200 for the sample variance and 14.142 for the sample standard deviation. I got all but the first one wrong. Can anyone show me the proper answer and how to get it? Thanks.

[JohnM]

Your average, midrange, and range are correct, as far as I can tell.

The avg deviation is 12. Subtract each value from 70 and take the absolute value. Add them up and divide by 5.

For the sample variance and std dev, you divided by n, and should have divided by n-1. Variance = 250, std dev = 15.811.

[orangeb]

Thank you for your help. I have another question if you don't mind answering it:
How do I determine the sample mean in the following problem?
The interval is: (10,20) The Frequency is: 2
(20,30) 4
(30,40) 2
(40,50) 1
(50,60) 1


Also, how do I determine the Mark for these?

Thank you!!!

What I have so far:

I have the Mark column as being 15
25
35
45
55

I have the cumulative frequency as 2
6
8
9
10
Did I do that correctly? The interval and the frequency were the only
numbers provided so I'm not entirely sure that I did the cumulative
frequency right either.
As for the Sample mean, I don't even know where to begin.

[JohnM]

Your class marks are correct, and you did the cumulative frequencies correctly.

To get the sample mean, use the method for "grouped data." Multiply each class mark by its frequency, add up these products, then divide this sum by the sum of the frequencies.

[orangeb]

Thank you for your help. You make these questions easy to understand. Is there anyway I can steal the math portion of your brain to get me through this class?

[JohnM]

No, but we're not going anywhere, so drop by once in a while....