[Tthip]

I need some help - anyone good with math?
In Excel when I figure out these two different equations - they come out different.
I have to figure out why.
Any help?

5/1/2006....... 262...... 19...... 7.2519%
5/2/2006....... 241...... 16...... 6.6390%
5/3/2006....... 226...... 21...... 9.2920%
5/4/2006....... 380...... 39...... 10.2632%
5/5/2006....... 164...... 16...... 9.7561%
5/8/2006....... 255...... 20...... 7.8431%
5/9/2006....... 266...... 32...... 12.0301%
5/10/2006...... 296...... 19...... 6.4189%
5/11/2006...... 211...... 9...... 4.2654%
5/12/2006...... 310...... 20...... 6.4516%
5/15/2006...... 180...... 14...... 7.7778%
5/16/2006...... 140...... 13...... 9.2857%
5/17/2006...... 202...... 22...... 10.8911%
5/18/2006...... 214...... 25...... 11.6822%
5/19/2006...... 242...... 21...... 8.6777%
5/22/2006...... 277...... 10...... 3.6101%
5/23/2006...... 222...... 15...... 6.7568%
5/24/2006...... 290...... 21...... 7.2414%
5/25/2006...... 281...... 15...... 5.3381%
5/26/2006...... 233...... 12...... 5.1502%
5/30/2006...... 284...... 35...... 12.3239%
5/31/2006...... 162...... 12...... 7.4074%
Total:............ 5338 ... 426

426 divided by 5338= 7.9805% ..... Average of the percents=8.0161%

Why are 7.9 and 8.01 different????

[D-man]

I would say it's likely a rounding error. The more digits you tell excel to keep, the better. I had a similar problem in my stats class last semester.

[robert goulet]

You can't take a percentage calculation of a percentage.

Example:
Tshirt $10.00 It's on Sale so you get a 5% discount, but today is the 10th anniversary of the store so every purchase gets an additional 10% discount on the final price.

You would assume that would mean a 15% overall discount...but watch

$10.00 X 5% discount = $9.50 now apply the additional 10% discount:
$9.5 X 10% discount = $8.55 final price


Whereas, were you to give a 15% discount off of $10.00 the price would be:
$10.00 X 15% discount = $8.50

The 2 numbers are close but they aren't the same.

So, to answer your question you have to go with your first calculation of 7.98% (depending on how many significant digits you want) rather than trying to get an average of percentages

[Pudge7681]

You're in luck. I am in fact a math teacher and can tell you that my students often times find these errors and get very confused. It is all due to rounding error. This little bit of error will make it raise the two tenths of a point or so that you are missing. The correct way to calculate it is the percentage of the totals not the average of the percents. It reminds me of the story of the engineer who foolishly did the same thing that you did and it resulted in the bridge's strength rating being nearly 100,000 pounds more than previously expected and hence the bridge collapsed...NOTE: This was not the same engineering team that created the Tacoma Narrows Bridge.

[Tthip]

Goulet - Pudge - Thank you very much.