1 and 5
The difference is between factor pairs and distinct factors. With square numbers, one of the factor pairs will be the same number twice. When listing the distinct factors, that number is only listed once.
How they're listed. The factors of 20 are 1, 2, 4, 5, 10, 20 The factor pairs of 20 are (20,1)(10,2)(5,4)
Factor pairs are just the factors of a number listed in a different way. The factors of 20 are 1, 2, 4, 5, 10, 20 The factor pairs of 20 are (20,1)(10,2)(5,4)
80 has 5 factor pairs.
The factor pairs of 215 are 1, 5, 43, and 215
The factor pairs of 10 are 1*10, 2*5
1 and 5
5 and 1
1 and 5
80 has 5 factor pairs.
The factor pairs of 25 are 1 x 25 and 5 x 5
1 and 5 is the only factor pair of 5.