Sooty, Sweep and Soo are going back to school the following week and Matthew has to buy two plastic folders, three biros, four pencils, five notebooks and ten coloured felt tip pens each for them. In order to work out how many of each item Matthew will have to buy, they have to use multiplication. But before they use multiplication, they have got to understand their numbers very well between 1 and 20, in other words they have got to be able to add and subtract.