Answer: They divided the numbers into the smallest numbers they could (prime factors) and then made matches between them.
Explanation:
Prime factors are the numbers that can't be divided. For instance, 10 can be divided into 2 x 5, but 2 and five can't be divided except by one, so 2 and 5 are prime factors.
What they did for 24 was basically divide it by two until they couldn't anymore. So, 24 divided by 2 was 12. You can write down 2 as a prime factor and then see how much more you can divide the 12 left over. Let's say 12 divided by 4 is 3. We can't divide 3 any further, so we can write it down as a prime factor with 2. Then 4 divided by 2 is 2. So, we can write down two more 2s with our other numbers.
Now we can write out all the prime factors we found: 2 x 2 x 2 x 3
When we do the same thing with 36 we get 36/12 = 3, 12/4 = 3, 4/2 = 2.
so, we have 2 x 2 x 2 x 3
and also 2 x 2 x 3 x 3
Now we can look at the two rows of numbers and find matching pairs.
We have two pairs of 2s and one pair of 3s. That means that 2, 2, and 3 are the common factors.
Even though there are two extra prime factors, we can't count those because they aren't in a pair. Also, you only say one number for each pair of prime factors. That's why it says 2, 2, and 3 instead of 2, 2, 2, 2, 3, 3.
Good luck:)