Wrong answer. As the question is what saves more fuel.

A saves 18 m.p.g.
B Saves 10 m.p.g.

Thus even though B has the biggest increase in percents, A saves the most actual fuel.
Indeed it can play tricks on your intuitions. In this case the percentage is very misleading.

ops, that should be A 20, B 10, thus even more so.

off course the original test takes the standpoint that you have a fleet of cars, and thus have to operate currently:
Compact + SUV
and you get to change one of those.
In which case it's better to replace the gas guzling SUV for a sedan.

Of course the real option then is to replace the SUV for a hybrid and really make some change

I see nothing wrong with a hybrid.. I actually wouldn't mind full electic, or even water fueled. Would save alotttt of money.

If you do the sums the way the Europeans do where economy is litres/100k the answer is obvious. To keep it simple and get reasonable size numbers we could use gallons/1000 miles ....

18 mpg -> 24 is 65 gal/1000 m to 42
- save 21 g/1000 miles

30 mpg -> 55 is 33 gal/1000 m to 18
- save 15 g/1000m

Cars that run on water and electricity certainly do.. And if it wasn't for greedy big oil we'd already be enjoying the benefit of higher technology.

I agree ptw.. It would have made more since to give the math for a as well. I'm with robert though, you might as well change the suv for a hybrid lol.

They've already got cars that run on hydrogen, and I believe they've got a car in japan that can draw the hydrogen from water. I saw a clip on it the other day. They've had this technology for years, but nobody pays attention to it.