1. Subtract the largest number with the smallest number... e.g. 100 - 25
2. Divide the range by 5 and 10... e.g 75/10= 7.5 75/5=15
3. Pick the number between 5 and 10... e.g. 7.5
4. Round to the largest whole number... e.g. 8
5. Add 8 to the smallest number of the range 5 times... e.g. 25 + 8, 33 +8, etc
6. You'll want to have it so the previous number becomes your beginning of your intervals... e.g. 25-33, 33-41, 41-49, 49-57, 57-65.
6. Fill your histogram