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Compare MPG average calculation

  #1  
Old 07-17-2008, 12:55 PM
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Join Date: Jun 2008
Location: Moore, Oklahoma
Posts: 118
Question Compare MPG average calculation

Question: I've entered 3 mileages in the database
50.4
54.3
55.9

By my calculation this should average out to 53.53 mpg
the datbase comes up with 52 mpg

What's up with that?
 
  #2  
Old 07-17-2008, 02:18 PM
Active Enthusiast
Join Date: Aug 2006
Location: San Jose, CA
Posts: 109
Default Re: Compare MPG average calculation

Trying adding the miles for all three tanks and dividing by the gallons for all three tanks. That will give you the real average.

True Avg MPG = (D1 + D2 + D3) / (G1 + G2 + G3)

Note this is different than what you calculated:

Fake Avg MPG = ((D1 / G1) + (D2 / G2) + (D3 / G3)) / 3

-dan
 
  #3  
Old 07-17-2008, 04:45 PM
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Join Date: Dec 2003
Posts: 4,623
Default Re: Compare MPG average calculation

That's correct Dan, thanks.

If you eat 1 hotdog in a year, then 1 hotdog in a month, then 1 hotdog in a day, how many hotdogs do you average per day? (Hint…it's not 1)
 
  #4  
Old 07-18-2008, 08:35 AM
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Join Date: Mar 2008
Posts: 45
Default Re: Compare MPG average calculation

Can't figure it out with the information provided:
How many days in a year? (365, 365.25, 366, or ?)
How many days in a year? (28, 29, 30, 31, or some average of these numbers)?
 
  #5  
Old 07-18-2008, 08:36 AM
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Join Date: Mar 2008
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Default Re: Compare MPG average calculation

Originally Posted by dpayne View Post
Can't figure it out with the information provided:
How many days in a year? (365, 365.25, 366, or ?)
How many days in a year? (28, 29, 30, 31, or some average of these numbers)?

The second line should be How many days in a MONTH?
 
  #6  
Old 07-28-2008, 07:44 PM
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Join Date: Jun 2008
Posts: 188
Default Re: Compare MPG average calculation

Originally Posted by dpayne View Post
Can't figure it out with the information provided:
How many days in a year? (365, 365.25, 366, or ?)
How many days in a year? (28, 29, 30, 31, or some average of these numbers)?
Highest average scenario (365 days for the year, then use February for 28, then have the last one on March 1st) comes out to 3 hot dogs in 394 days, or 0.00761421320 hot dogs per day.

Lowest average scenario (Leap year, a month with 31 days, then the final day) comes out to 3 hot dogs in 398 days, or 0.00753768844 hot dogs per day.

For those of you keeping score at home, that's a variance in average of 0.00007652479 hot dogs per day. I'm thinking the difference only works out to a couple poppy seeds on the bun.

("Why?" I hear you ask. I don't know, probably for the same reason a group of us sat around in college in the '80's and figured out the explosive power of a photon torpedo launched from the Enterprise and determined it would be enough energy to blow a battleship to the moon.)
 

Last edited by tbone526; 07-28-2008 at 07:47 PM.
  #7  
Old 07-29-2008, 05:04 PM
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Join Date: Apr 2008
Posts: 497
Default Re: Compare MPG average calculation

Originally Posted by mdarmistead View Post
Question: I've entered 3 mileages in the database
50.4
54.3
55.9

By my calculation this should average out to 53.53 mpg
the datbase comes up with 52 mpg

What's up with that?
You can not take an average of averages. Clearly the tank in which you got 50.4 mpg had more miles than the other tanks so it is weighted heaver by the database, as it should be.
 
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