[Geo Metropolis]

Math is not my strong suit, does the following sound correct more or less?
Let's say my range is 400 miles on my 8 gallon tank (which it often is).
Let's say gas weighs roughly 8# per gallon.
If I do 400 miles I would imagine I carry on average 4 gallons or 32# of fuel.
Now lets say I do a half fillup.
This would allow me another 200 miles carrying an average of 2 gallons or 16# of fuel.
For the combined trip I would have been carrying 32#s 66% of the time and 16#s 34% of the time.
By my calculations that's 600 miles carrying an average of 26.5#s of fuel.
32-26.5=5.5#s saved. Not the most impressive ever, but think about bigger tanks, or if you did this for an extended period of time with multiple one or two gallon fills. Food for thought...