# Compare MPG average calculation

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**1**Hybrid Evangelist

Thread Starter

Join Date: Jun 2008

Location: Moore, Oklahoma

Posts: 118

**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?

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?

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**2**Active Enthusiast

Join Date: Aug 2006

Location: San Jose, CA

Posts: 109

**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

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

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**5**Enthusiast

Join Date: Mar 2008

Posts: 45

**Re: Compare MPG average calculation**

The second line should be How many days in a MONTH?

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**6**Active Enthusiast

Join Date: Jun 2008

Posts: 188

**Re: Compare MPG average calculation**

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.*

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**7**Super Moderator

Join Date: Apr 2008

Posts: 497

**Re: Compare MPG average calculation**

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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