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22/7 is a pretty decent choice for teaching 11-year-olds about fractions that are close to pi. 355/113 would be better, if you think they can remember numbers that big. And approxRational is fun. Exercise for the interested reader: implement an inverse to approxRational.
And tiny-tim has a point. You wouldn't change it in terms of [itex]\pi[/itex] because your answer is obviously approximated and most likely since you had to approximate the answer, it's not going to be a nice fractional radian value such as [itex]\pi/4[/itex] etc. #10. tiny-tim Science Advisor.