HELP! Doesn't make sense

#1
I am stumped. I have a problem with trying to figure out call-time statistics at work. I have data plugged in and totals are all correct. Here is an example.

number of calls: 35
number of minutes total: 190
Average talk time: 5.428571

I get these totals from the following 6 data sources

first line: 6 calls 31 minutes 5.166667 avg
second line: 8 calls 22 minutes 2.75 avg
third line: 5 calls 40 minutes 8.0 avg
fourth line: 7 calls 41 minutes 5.857143 avg
fifth line: 2 calls 16 minutes 8.0 avg
sixth line: 7 calls 40 minutes 5.714286 avg

Here is my problem: When I add together the individual numbers the call totals and number of minutes add up, but I cannot get the same average. When I add together the average talk times from my individual numbers, and then divide by number of lines I get an average talk time of 5.914683. This does not match the average from the totals of 5.428571. What am I doing wrong?
 

vinux

Dark Knight
#2
You have to take weighted average here. like ( 5.166667 x 6 + 2.75 x 8 + 8 x 5 + 5.857143 x 7 + 8 x 2 + 5.714286 x 7) / (6+8+5+7+2+7 )

You can't take the average of averages Since here in each line the number of calls are not the same.
RIch