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Stoichiometry question


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"Compound Y is a hydrocarbon and has a molar mass of 86.20 g mol–1. Upon combustion, Y produces 1.75 g CO and 0.836 g H2O.
Deduce the molecular formula for Y."

This is a question I tried solving yesterday, related to Stoichiometry. It's simple enough and I understand the general way to solve this. After calculating both n(C) and n(H), I tried calculating n(C)/n(H). My problem is that this resulted in something like this: 

0.0398/0.0928 = 199/464 (=0.4288...)

The solutions that are available to me say it's more like 3/7. Now, my question is probably more related to math and calculators than chemistry itself. I can't seem to get this approximation of 3/7 with my TI - Inspire calculator. It just gives me the fraction shown above with an approximation of the decimals. Is there some sort of trick I can use mathematically, or should I be able to tell just by looking that it is around that average. A more universal method would be appreciated.

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