A factor is a number that can be evenly divided into other whole numbers without having a remainder left over. For example, 9 is a common factor of 1, 3 and 9. Fractions and decimals are not found in common factors making finding common factors rather easy.
A common factor is a number that can be evenly divided into a collection or series of whole numbers. For example, the number 1 is a common number that can be evenly divided into any series of whole numbers.
Finding the factors of a whole number begins with starting with the number “1” and then dividing it with the given number. For example, let’s say that our given whole number is “9”.
9 ÷ 1 = 9
We see that when we divide “9” by “1” we get a whole number, i.e., “9”. We then continue to divide the number “9” with each ascending number as follows:
9 ÷ 2 = 4.5
9 ÷ 3 = 3
9 ÷ 4 = 2.25
9 ÷ 5 = 1.8
9 ÷ 6 = 1.5
9 ÷ 7 = 1.28
9 ÷ 8 = 1.12
9 ÷ 9 = 1
Once you divide the whole number into itself, this will give you the last factor. The last factor of 9 is “9”.
The factors of 9 are then, 1, 3 and 9 because the answer derived is a whole number. 2, 4, 5, 6, 7 and 8 are not factors because they did not divide evenly and the answer included either a fraction or decimal.
The highest common factor is when you take two or more whole numbers and then locate the highest common factor found in each number. For example, the highest factor of 9 is “9”. Now let’s compare that with the whole number 6.
6 ÷ 1 = 6
6 ÷ 2 = 3
6 ÷ 3 = 2
6 ÷ 4 = 1.5
6 ÷ 5 = 1.2
6 ÷ 6 = 1
The factors of 6 are 1, 2, 3 and 6. The highest factor of 6 is “6”. Now, which common factor of 6 matches the factors of 9? As we can see, both the numbers 1 and 3 are factors of the whole numbers 6 and 9. Now of the 1 and 3, which is the highest factor? The answer is “3”. 3 is the highest common factor.
18 ÷ 1 = 18; 18 ÷ 2 = 9; 18 ÷ 3 = 6; 18 ÷ 4 = 4.5; 18 ÷ 5 = 3.6; 18 ÷ 6 = 3; 18 ÷ 7 = 2.57; 18 ÷ 8 = 2.25; 18 ÷ 9 = 2; 18 ÷ 10 = 1.8; 18 ÷ 11 = 1.63; 18 ÷ 12 = 1.5; 18 ÷ 13 = 1.38; 18 ÷ 14 = 1.28; 18 ÷ 15 = 1.2; 18 ÷ 16 = 1.12; 18 ÷ 17 = 1.05; 18 ÷ 18 = 1
The factors of 9 are 1, 3 and 9. The factors of 18 are 1, 2, 3, 6, 9 and 18. The factors that can be found in both 9 and 18 include the numbers 1, 3 and 9. 9 is, therefore, the highest common factor so Answer (a) is the correct answer