Advertisement

Now, we got to 2...  It's prime, so we circle it and go through the entire list and cross out all numbers that 2 goes into.

A grid of the numbers 1 - 100  ...  circle the 2 and cross out any other numbers that 2 goes into.

 

Now, we go to the next number: 3

If it hasn't been crossed out yet, it's prime!  Circle him... then, go through and cross out all the numbers that 3 goes into (which is every third number).
 

A grid of the numbers 1 - 100  ...  circle three and cross out any other numbers that 3 goes into.