More Activities on the 100s Chart

Update: To download a free 100 chart that will accommodate many math material cubes, click here.

Today's freebie is really two activities that you can have students do with the 100s chart.  The first one is called the Sieve of Eratosthenes.  Students take a chart and shade in all the multiples of 2 (not counting 2).  Then they shade all the multiples of 3 on the same chart (not counting 3).  They should notice that all the multiples of 4 have already been shaded when they shaded multiples of 2, so they continue with multiples of 5. The multiples of 6 have already been shaded, so finish up the chart with the few multiples of 7 that have not already been shaded.  The multiples of 8, 9, and 10 will already have been shaded.
 
The result should look something like this:

Those that are left uncolored are the prime numbers.  Prime numbers have exactly two factors, one and itself.  Composite numbers have more than two factors.  One is neither prime or composite.

Once students have completed this chart, they can use it to develop strategies for the Factors and Multiples Game.  I introduced the Factors and Multiples Game on my blog a couple of months ago.

Activity number two is a variation on the game.  Like the original version, the first player chooses an even number less than 50.  The second player chooses a number that is either a factor or multiple of the first player's number.  Instead of using strategies to choose a number that has no uncovered factors or multiples, the students work cooperatively to create the longest factor/multiple chain.  Teams record their chains on a class chart and see who can create the longest chain.

I hope you and your students enjoy these activities.