# Greatest Common Factor

## The 5-step plan

To simplify fractions, you need to look for the greatest common factor, also called the GCF. This is the highest positive cardinal number both the numerator and denominator can be divided by, without leaving remainders. This skill is important and you need to master it before you can continue with other fractions exercises, such as multiplication and division with fractions. In the 5-step plan we look for the GCF. At step 1 you get 10 open questions. At step 2 you can drag the answers. At step 3 there are more open questions, but more difficult than at step 1. At step 4 you get multiple choice questions, and at step 5 you need to get the diploma.

### Step 4 - Multiple choice, choose the GCF

Try to answer all the 15 questions right!

### Step 5: Get your diploma

Answer all the 20 questions right to get the diploma!

## Description Greatest Common Factor

How do you find the greatest common factor? Example: 20 and 40. First write down all the factors of 20: 1, 2, 5, 10, and 20. And then those of 40: 1, 2, 4, 5, 10, 20, and 40. Now look for the highest number in both lists. That's 20. The greatest common factor of 20 and 40 is 20.
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