Range. The range is the difference between the biggest and the smallest number. To work out the range: Put the numbers in order: 3 6 6 6 7 9 11 11 13. Subtract the smallest number from the biggest number: 13 - 3 = 10. So the range of this set of numbers is 10.1  Page: 2  1. 3  2.o work out the range: Put the numbers in order: 3 6 6 6 7 9 11 11 13. Subtract the smallest number from the biggest number: 13 - 3 = 10. So the range of this set of numbers is 10. 1  Page: 2  1.