Maths help needed - TTLG Forums

PigLick on 22/2/2016 at 11:14

Ok my son is doing some high level maths which I have no idea about (cos I dumb). He is having trouble, can anyone help out here at all?
This is the question (its about prime factors and such) : Find the highest common factor of 17,325 and 14,553.
Its not so much the answer itself but how do you arrive at said answer?

Jason Moyer on 22/2/2016 at 11:37

Looking at good old Mr Google, you break down each number into prime factors, then find shared prime factors:

14553 = 3^3*7^2*11
17325 = 3^2*5^2*7*11

The common prime factors are 3^2*7*11 = 693

demagogue on 22/2/2016 at 11:38

Google answered this quickly enough, but granted not in one nice package. First you get the prime factors for each number ((http://www.mathsisfun.com/prime-factorization.html)) by dividing it by increasing prime numbers that leave no fractions, then divide the remainder by higher primes, etc, until you're left with a string of prime numbers for each number that, when you multiply them all, you get that number. Then you mark the prime numbers they have in common, multiply them, and that's your answer ((http://www.cimt.plymouth.ac.uk/projects/mepres/book8/bk8i2/bk8_2i4.htm)).

WingedKagouti on 22/2/2016 at 11:50

The simple way is to find all prime factors for each of the two numbers, then compare the two lists.

17325 = 3*3*5*5*7*11
14553 = 3*3*3*7*7*11

So in this case: 3*3*7*11 = 693, 693*5*5 = 17325, 693*3*7 = 14553

Finding the primes can be done in different ways (you can find some discussion (http://math.stackexchange.com/questions/631559/algorithms-for-finding-the-prime-factorization-of-an-integer) here), but since you're asking on behalf of your son, I think something like (http://www.mathsisfun.com/prime-factorization.html) this may be of more immedate use.

PigLick on 22/2/2016 at 12:12

thanks a lot for your help, those sites helped a lot.

demagogue on 22/2/2016 at 12:13

I'm gunning for a 4th sap currently answering this. Just you wait...

Edit. well ok, a ninja post like that will do as well. ;)

PigLick on 22/2/2016 at 12:37

my son is also in the schools chess club, and regularly beats me when we play ;)

faetal on 22/2/2016 at 13:00

Is he always so violent?

Kolya on 23/2/2016 at 12:40

All's fair in love and battle chess.

nobodyinparticular on 25/2/2016 at 16:24

I cannot move for all the scurrilous innuendo in here.