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Math Objective  To show students how least common multiples are achieved using two and three numbers. 
Skills/Outcomes 

Files to Use Download Info/Instructions  lcm.doc lcm.xls 
Optional Resources  calculators 
ClassroomDiscussion and Activities
Computer Lab Activities
ClassroomDiscussion and Activities
Teacher Note: This activity should not replace traditional paper and pencil methods for finding common multiples, especially for the numbers frequently found in denominators of fractions. 
When the purpose of teaching common multiples is to find the leastcommon multiple for fractions, the numbers used should stay withinthe range of fractions encountered in normal life. Students shouldthen be working with denominators of 2, 3, 4, 5, 6, 8, 16, 12, and10.
It may be helpful to have students organize their searches forcommon multiples on a grid such as the one below. The top number isthe factor used to multiply the numbers in the problems. An exampleof this kind of student worksheet is available in lcm.doc.
Find the least common multiple for 6 and 15.
This grid will provide a natural transition to the spreadsheetactivity. You can use calculators to have students complete exerciseslike the one above. Just multiply row and column numbers (e.g., 6 x2, 6 x 3) and fill in the grid. The next step is to look back overthe series and find the common number. In this case, it would be 30.This practice provides a foundation for common multiples.
To prepare the computer activity, give students a blankspreadsheet grid. These can be found in grid wksht. Have themwrite the formula in cells B2 and B3 as shown below, using thenumbers in the problem (in this case, 6 and 15) as the constants.Tell them that in the lab, they will use the FILL RIGHT command tocopy the formula over as many places as needed. You may want studentsto write this command in the cells to the right of the formulas sothat they remember.
ComputerLab Activities
Teacher Note: Here's a formatting tip. It is helpful to use colors and borders to help keep the different multiples separate from the factors. We have set up some sample exercises like this in lcm.xls. 