Lattice Method for Multiplication (grades 3 and up)

Introduction

This method of multiplication is shown by using a table. The size of the table depends on what the size of the numbers are that you are multiplying. For instance, if you were multiplying 486 times 45, your table would be a three by two table. The table would be split into three columns and two rows. Each litte cell that the table is split into, the cell itself is split diagonally from the top right corner down the bottom left corner. The three digits of the first number would be split so that the 4, 8, and 6 are above each of the columns and the 4, and the 5 are split on the right side of each row. After you have completed the table and placing the numbers in their correct places, you begin multiplying. First, you will multiply the 6 (from 486) and the 4 (from 45). The product of this multiplication problem (which is 24) will be places in the very top right cell and where the diagonal line splits the cell, it will also split your number. In the top section of the cell will hold your 2 and the bottom of the section will hold your 4. Moving on to the next numbers, you will multiply the 8 (from 486) and the 4 (from 45). You will continue the same process as before. Next you will multiply the 4 (from 486) and the 4 (from 45). This wil complete your first column of numbers. Moving on to the next column, you will multiply the 6 (from 486) and the 5 (from 45) and continue multiplying each number in 486 by the 5 from 45 until you have multiplied all numbers. Once you have completed all of the multiplication of these numbers, you will notice that they are diagonal rows of numbers starting from the right and moving left. You will add all of the numbers up in each row and the units digit of that number will be placed below each diagonal row. (If the sum of the numbers is larger than 9, the tens digit will be carried over into the next diagonal row). For instance, the very first diagonal row we will be adding only has one digit in it so that one digit gets carried down (which is a zero). You will continue to add up each row (and remember to carry over the tens digit if the number is bigger than 9) until you have a number under each diagonal row. In this situation, your final answer should be 21,870.

Task

Here are some multiplication problems you can try:

768 x 564

908 x 321

439 x 748

Process
Evaluation
0 1 2 3
Completion of Problems
Correction of Problems
Neatness and Effort

(0 being the worst you could do, 4 being the best you could do)

Conclusion

I'm hoping this Webquest was successful in teaching you how to implement the Lattice method!