math1

Using VERTICALLY AND CROSSWISE you do not need to the multiplication tables beyond 5 X 5.

• Suppose you need 8 x 78 is 2 below 10 and 7 is 3 below 10.
  Think of it like this:
  
  The answer is 56.
  The diagram below shows how you get it.
  
  You subtract crosswise 8-3 or 7 - 2 to get 5,
  the first figure of the answer.
  And you multiply vertically: 2 x 3 to get 6,
  the last figure of the answer.
  That's all you do:
  See how far the numbers are below 10, subtract one
  number's deficiency from the other number, and
  multiply the deficiencies together.
• 7 x 6 = 42
  
  Here there is a carry: the 1 in the 12 goes over to make 3 into 4.