advertisement

A Quick Method to Multiplying 2 Digit Factors Up to 20 Investigation # 7 Submitted by: Ethel L. Jones In 3rd and 4th grades there must be constant efforts to allow the students ways to memorize and understand multiplication and division facts. The mastery of division begins with a firm grasp of multiplication. It is a struggle for children to retain multiplication facts. Therefore, it is important that they be given alternative methods to arrive at answers. The particular shortcut will benefit both, the weak student as well as the more able student. It will review addition facts while working on multiplication facts of factors up to 20. It will also reinforce skills in the area of place value. The author, Vic Evans, wrote to always make sure that the bigger numbers were on top. It was observed in this investigation that as in any other multiplication process, this did not seem to make a difference. However, for the sake of any error, the directions were carried out in multiplying any two numbers from 11to 19 without the use of a calculator: http:www.angelfire.com/me/marmalade/mathtips.html Examples: Take 15 X 13 Cover the 15 and the 3. These covered numbers are all that will be used. Add 15 + 3 Add a zero to that sum. ( Multiply it by 10) Multiply the lower number ( 3) by the number directly above it (5). Add the two numbers together. (180 + 15) . That is the answer. 15 X13 15+ 3 =18 5X 3 = 15 10 X 18 = 180 Add 15 195 Check: 15 X13 45 15 195 17 X 15 17 + 5 = 22 X 10 = 2 2 0 5 X7 = 35 35 255 Check: 17 X 15 85 17 2 55