The factors of 100 are 1, 2, 4, 5, 10, 20, 25, 50, 100. Calcating the factors of 100 is straightforward. 100 and 1 are the easiest two factors to find.
Try 1. 1 x 100 = 100, so put these into our factor list.
1
...
100
Take 2. 2 x 50 = 100, which means we add these to our factor list.
1
2
...
50
100
Now take 3... no. 100/3 isn't a whole number. So we skip 3.
Next try 4. 4 x 25 = 100, so we add these to our list of factors.
1
2
4
...
25
50
100
Now try 5. 5 x 20 = 100, so put these into our factor list.
1
2
4
5
...
20
25
50
100
Try 6... no good. 100/6 isn't a whole number. So we skip 6.
Take 7... no. 100/7 isn't a whole number. So we skip 7.
Now take 8... no luck. 100/8 isn't a whole number. So we skip 8.
Next try 9... nope! 100/9 isn't a whole number. So we skip 9.
Now try 10. 10 x 10 = 100, so we add it to our list of factors. There are no numbers between 10 and itself, so we can stop.