You would agree with us that the more you use your organs/parts of the body the more it responds and more becomes the efficiency of that particular organ. For example:- If you were to start jogging it would be most probable that you would be able to run a Kilometer, but if you were to jog for two years you could increase this to 15 kilometers per day. If we exercise any body part then its efficiency increases ,this fact is implies to our brains also, now the question is how do we give exercise to our brains? Mathematics is good medium for exercising our brains. Scientists have proved that mental arithmetic of higher level e.g. 76382*793 = ?, can give lot of exercise to our brains hence it is the best medium to exercise our brain.