   The Number Wall App The Number Wall App is available for iPhone and iPod (requiring iOS6 at least). It offers you a lot more possibilities than the mere addition of numbers: Immediate verification of results You get immediate feedback whether you calculated correctly or not: the background of the field in question will be colored red if the result is not correct. Calculation with positive and negative numbers You may choose to calculate not only with positive numbers but with negative ones as well (what's called "whole numbers"): 7+(-9)=-2 or 3⋅(-7)=-21 Fractional calculus Add fractions: 3/7+4/5=(15+28)/35=43/35 It is not necessary to simplify a fraction (if possible) for the result to be accepted as correct. Modular arithmetic This means that you don't calculate with the numbers themselves but with their remainder after division by a given number (the divisor). In fact you do it all the time: 5 hours after 10 a.m. is the 15th hour of the day or 3 p.m.; that is the remainder of 15 divided by 12. Modular arithmetic is indicated in the Number Wall by e.g. +/17 showing in the background of an empty field. Which, in this case, means you should add remainders of numbers divided by 17 (also called "modulo 17"). Then, for example, the result of 2 + 16 is not 18 but 2 + 16 = 1 Use help If you don't know the result of, say, 56⋅75 or 7/12+23/45, you can get help by writing =56⋅75 and =7/12+23/45 respectively into the field in question. The result then will show up and the background of the field will be colored yellow. Perhaps you are familiar with these kinds of formulae from spreadsheets (like Excel). Due to the great diversity of possible calculations, the Number Wall App is interesting, challenging and instructive from elementary school age up to the first years in secondary school. © jweckler.de 2019 | Impressum | contact@jweckler.de