Friday, February 08, 2008
In the spirit of mathematical quirks, here is another trick. When mutiplying by 9, hold up both hands and put down the finger corresponding with the number you're multiplying by. Then count the number of fingers to the left and right of the finger that is down and you'll have the respective ten digit and single digit number for 9 times X. So for example if I were multiplying 9 x 7, I would hold down the index finger on my right hand. There are 6 fingers/thumbs to the left of the index finger which is down and 3 fingers to the right. So 9 x 7 according to our finger calculator is 63. Doing a little math by hand, if you will.