[cheeseeeeee]

In maths I need to know what --- this means... a rule for the lowest common multiple when is it the pair times together?

[mathwiz3502]

LCM is the least common multiple usually referring to 2 numbers.
A way to find LCM is to get both numbers' prime factorization.
Now write the numbers in common below (the two #s count as one).
Then write the numbers left out and multiply it all.
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[Unknown008]

It's the least common multiple. For example, the multiples of 2 are 2, 4, 6, 8, etc. Those of 14 are 14, 28, 42, etc. The lowest multiple that both 2 and 14 have is 14.

I'll give you a practical example.

Say a drop drips from a certain tap each 10 seconds. Another tap drips a drop each 15 seconds. At the start, both drips a drop. At which time will they drip a drop at the together again?

Well, to find that, you use LCM.
The multiples of 10 are 10, 20, 30, 40, 50, 60, 70, etc
Those of 15 are 15, 30, 45, 60, 75, 90, etc.

You'll see that the lowest one is 30 (both have 30, hence the term 'least common multiple').

That means at 30 seconds after the start, both will drip together!

You'll also notice here that is it each 30 second that they drip together.

[g13544055]

mathwiz is right, get their prime facorisation, remember.. any integer can be represented as a product of prime factors, that's the fundamental theorem of arithmetic, should check it out. If it's a pair of numbers, just break it down into this (ie 36=4x9=2x2x3x3=2^2 x 3^2), and pair of unique numbers.

[elscarta]

While you are all correct the post did not ask how to find the LCM but "when is the LCM the pair of numbers multiplied together?"

This occurs when they are co-prime. That is when they have no common factors except 1.

[Unknown008]

Sorry, I didn't understand that part the OP was asking :o

[g13544055]

True elscarta. Two numbers a and b,

ab=gcd(a,b)lcm(a,b)
so for lcm(a,b)=ab, gcd(a,b)=1, i.e. coprime!