You can count by fives by adding five to the previous count.
If you start with an zero then each number will end in either 5 or 0.
The numbers that you would count if you started with 0 and counted by
fives would be:
0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,
90, 95, 100.
If you start the count with another number, then just add five to the
last count. For example:
1, 6, 11, 16, 21, 26, 31, 36, 41, 46, 51, 56 and so on.
Notice that there is a regular pattern in these counts. Every
other number ends with the same digit.