The more painstaking way would be to divide up the spinner up into 100 pieces, and shade in 5 of those pieces. Since 5/100 = 0.05 = 5% this means that landing on any of the 5 pieces has a 5% chance of happening. A better way to do this is use 20 slices instead. This works because 5/100 reduces to 1/20 (divide the top and bottom by 5 ). Instead of shading in 5 slices, Mark should shade in 1 . Using a calculator, you should see that 1/20 = 0.05 = 5% as well. The second option is more common but even then a spinner with 20 sections is still a lot. It will be much better for Mark to pull some random numbers out of a hat or anything other accessories, or let a computer generate random numbers.