To find all possible answers, we can start by listing all the numbers between 10 and 20, and all the numbers between 20 and 40, and then check which pairs of numbers have a highest common factor of 4.
Numbers between 10 and 20: 10, 11, 12, 13, 14, 15, 16, 17, 18, 19
Numbers between 20 and 40: 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40
To have a highest common factor of 4, both numbers must be divisible by 4. Therefore, we can eliminate any numbers in these lists that are not divisible by 4.
Numbers between 10 and 20 that are divisible by 4: 12, 16, 20
Numbers between 20 and 40 that are divisible by 4: 20, 24, 28, 32, 36, 40
Now we can check which pairs of these numbers have a highest common factor of 4.
some possible answers are:
12 and 20
12 and 24
12 and 28
12 and 32
12 and 40
16 and 20
16 and 24
16 and 28
16 and 32
16 and 40
20 and 24
20 and 28
20 and 32
20 and 36
20 and 40
there are more answers, all you have to do is to pair 2 numbers.
if you do not want to include 20 and 40 make sure to not chose them.
Hope this could help.