Learn to add and subtract in your head by imagining an abacus to calculate the result. This workbook has 1882 problems with answers. Example: Learn to calculate 415-350+233-155+44 quickly, just by imagining an abacus. To follow this course you will also need: 1) A Japanese abacus (with at least 13 columns). 2)The accompanying Instruction book 'Imaginary Abacus - Instruction book' (sold separately). Clearly written with graphics. Answers to all work is included. Learning to use an abacus is both enjoyable and helps to improve concentration and memory power. Clearly written with graphics. Answers to all work is included. Learning to use an abacus is both enjoyable and helps to improve concentration and memory power.