### Video instructions and help with filling out and completing section 321: entry type 86

**Instructions and Help about section 321: entry type 86**

There are many ways in which we can find the HC F of two numbers but in this video we will look at the prime factor method let's say we want to find the HC f of 24 and 36 what we need to do is very simple we just have to reduce the numbers to its prime factors and we can do that using upside-down division first let's find the prime factors of 24 we draw two lines like this now we think of all the prime factors that 24 is divisible by we start with 2 24 is divisible by 2 so we write a 2 here 2 times 12 is 24 what about 12 is it divisible by 2 yes 12 is also divisible by 2 we write 2 again and draw a line 2 times 6 is 12 6 is also divisible by 2 and 2 times 3 is 6 we stop here as we got a prime factor how can we write 24 now remember the l-shape 24 can be written as 2 x 2 x 2 x 3 we reduce 24 to its prime factors we do the same for 36 actually why don't you try reducing 36 to its prime factors pause the video and give it a shot 36 is divisible by 2 and 2 times 18 is 36 18 is also divisible by 2 and 2 times 9 is 18 is 9 divisible by 2 no 9 is not divisible by 2 and we jump to the next prime number which is 3 is 9 divisible by 3 yes 9 is divisible by 3 3 times 3 is 9 we stop here since it's a prime factor 36 can be written as the product of these 4 numbers 36 is equal to 2 multiplied by 2 x 3 x 3 the difficult part is over but how does this give us the HCF to find the 8 CF all we have to do is multiply the prime factors that are common to both the numbers 2 is a common prime factor to both the numbers so we write a 2 once there is another 2 that is common to both so we multiply this 2 with another 2 and there is a 3 which is common to both the numbers as well hence we multiply this product with 3 yes we just multiplied the prime factors which are common to both the numbers this gives us the HCF 2 times 2 is 4 and 4 times 3 is 12 the highest common factor of 24 and 36 is 12 this is the prime factor method to find the highest common factor of two numbers in the next session we will solve for the 8 CF of 42 and 56 Music you