What's the average of 5 MPG and 10 MPG?
The math isn't quite obvious to me, but if you go out camping and get 5 MPG on the way to the campground and turn around and get 10 MGP on the way back, your average MPG won't be 7.5 as you would expe...
Forum Discussion
bob_nestor wrote:
Taking an average of averages is mathematically incorrect and almost always leads to a non-senssical answer.
So the (5 MPG + 10 MPG)/2 giving the 7.75MPG is wrong. As OldBiscuit pointed out you need to back out the average to get to the original data sets and combine them to correctly calculate the true average.
It's a bit like that old math puzzle: 3 men go to a hotel and rent a room for $30 where they each pay $10. The desk clerk realizes the room is only $25 so he sends the bellboy to their room with a $5 refund. The bellboy realizes he can't split the $5 evenly, so he pockets $2 and give each man $1 back. Now the men have each paid $9 for the room ($10 - the $1 they got back), for a total of $27 and the bellboy pocketed $2 for a grand total of $29. Where did the other $1 go?
They each paid $8.33 to get to $25 ... so each man actually paid $9.33, not $9.00 ... OR, one paid $9.00 and the other two paid $8 each ...
