Nevermind, I got it. I misread your question. You want frequency means and standard deviations. That works like this:
Multiply each time interval, the maximum one, by the frequency. You should get:
This adds up to 960. Now, the total frequency is 30, so mean is 32.
No, I guessed that had something to do with the lenghts. Because when you put in the answer it has _______lengths. I havn't done that yet.
The problem is, I have to get over 70%. I must keep trying until I do. Every time I re-do the test, the data changes, and it becomes hard to work out whast I could be doing wrong.
You may want to read through the probability and statistics forum on this site for other insight. http://www.mathhelpforum.com/math-he...ty-statistics/
There are some very good threads on statistics and methodology. I'd read through some of the old threads as well, very useful material!