What is the concept behind solving this senior school certificate math question?

[mathelord]

I just wrote my senior school certificate exam ,but could not solve one of the maths questions .the question is as follows
3 night quard a,b,c blow their their whistle at intervals 8,15,and 18 minutes respectively.if they blow together at 11.00 p.m,when next are they expected to blow together

 

[HallsofIvy]

8= 2*2*2, 15= 3*5, and 18= 2*3*3. The least common multiple of those is
2*2*2*3*3*5= 360 which is 6*60 or 6 hours. They will all blow their whistles together again at 11+ 6 hours or 5:00 a.m.

 

[mathelord]

I don't not get it ,on wat principle of maths or wat branch is this on

 

[whozum]

Lowest common multiples and greatest common factors.

 

[HallsofIvy]

The "branch of mathematics" is arithmetic!

 

[uart]

I don't not get it ,on wat principle of maths or wat branch is this on

Yes it's just a lowest common multiple question. Basically you need to have every prime factor from each number repeated to the maximum power that it appears in any of the individual numbers.