"Stacked" fractions? You mean common or vulgar fractions? Why not? Because you can't get your pocket calculator to display them?
I like them here because, the question being one of approximation, "1/3 km" is a lot more like the right answer than the falsely precise "336 m".
I once asked this question on a freshman chemistry exam:
"A gross of potatoes weighs 64 pounds; a gross of grapes weighs 2.4 pounds. How many pounds of potatoes do you need in order to have as many potatoes as there are grapes in 0.6 pounds of grapes?" And then, just to provide unnecessary (but confounding) information, I added "1 gross = 12 dozen = 144".
If you try to solve this problem by actually
using the additional info and a pocket calculator, you tend to get answers with repeating decimals that you have to round off. If you have a cheap fixed-point calculator, you get
wildly wrong answers -- at least, my students did. If you treat it as a problem of ratios, though: X/64 = 0.6/2.4, you get the answer "16" almost by inspection.
(If you're wondering why this was on a chemistry exam, it's because it's a "mole" problem, stripped to its essentials and talking about grapes and potatoes instead of, say, oxygen and uranium.)
My students were pissed off at me; I was pissed off at them, because most of them, it seemed, didn't know how to divide 64 by 4.
It's the wording, of course, that's at issue; I'm sure (I
think) that if I had asked "How much is 64 divided by 4," most of them
would have got the answer, even without a calculator. They were, after all, just college students, and probably hadn't yet forgotten all their arithmetic.
improper 
Linear Mode
