Help with maths homework question please!

[Ginorchoc]

Hello can anyone help with this maths question as I'm rubbish at maths and don't remember doing this in school (over 20 years ago )

Train 1 leaves the platform at 8.10 and leaves every 15 minutes. Train 2 leaves the platform at 8.10 and leaves every 20 minutes. What time do they both leave the platform at the same time. We worked this out to 9.10.

The question is what is the HCM ?

HCF!

8.10 8.10
8.25 8.30
8.40 8.50
8.55 9.10
9.10

So every hour because 4 x 15 is 60, 3 x 20 is 60
So at 10 past every hour they will both be there.

Perfect thank you really appreciate it.

Hcf as in highest common factor? Of 15 and 20, that will be 5. But I'm unclear what that has to do with the train question, so im probably wrong.

I think the question is about LCM not HCF.

www.mathsisfun.com/definitions/least-common-multiple.html

www.mathsisfun.com/definitions/highest-common-factor.html

It def says HCF. Im terrible at maths so my daughter has no one else to ask if she struggles.

Is train question not related to HCF?
Since LCM in 15 and 20 is 60, and HCF in 15 and 20 is 5, it doesn't make sense to solve train question, imo.

OK think it may be a part answer.
The product of prime factors for 15 are: 3 x 5
The product of prime factors for 20 are: 2 x 2 x 5

HCF is 5
LCM is 2 x 2 x 3 x 5 = 60