The topic of Estimation and Approximation from the Year 9 book of the Mathematics Enhancement Program. For information about these resources and an index for the whole collection please visit http://www.mrbartonmaths.com/CIMT.htm Keywords: Rounding, Decimal Places, Significant Figures, Size, Ten, Unit, Hundred, Tenth, Hundredth, Integer, Whole, Error, Bound, Upper, Lower, Propagation, Calculator.