Another maths problem! (three bus services)

[SouthWiltsGrammer]

Three bus services stop at my bus stop. Service A departs every three minutes, service B every 5 minutes and service C every 8 minutes.

If all three services leave my stop at 10.00am at what time will they next leave my stop together?

How would a child work through this answer quickly? What method would be used?

[Sally-Anne]

It is the Lowest Common Multiple of all three numbers.

3 x 5 x 8 = 120.

120 minutes is two hours, so the answer is 12:00.

[moved]

To encourage understanding I would choose two small numbers first, e.g. 2 and 3
Your child can then count in 2s and 3s to get to 6.
Do this a couple of times and then do the same with 3 nos, e.g. 2, 3 and 4.
That way DC isn't merely applying a rule to one situation, s/he is building up skills for other problems.

[SouthWiltsGrammer]

I don't see how the poster that helped me above Sally-Anne would have known to do that I wish I was better at Maths, I have mild dyslexia which I think affects me working out maths easily. It isn't making it very easy to help my DD. She does have a tutor but I like to help at home too.

[moved]

Post on here and ask for ways to support your DD best. Lots of us will help.

[SouthWiltsGrammer]

Thank you Moved I appreciate that very much.

[russet]

To help the child visualise the problem you could try this:

Cut a piece of graph paper into strips.
On one strip colour in every other square.
On the next strip colour in every third square.
If you then line up two of the squares you can then see how many squares before they line up again.

You could then try it with three strips of 2, 3 and 5.

Get the child to look at what happens with say 6 and 9.

[equilibro]

To encourage understanding I would choose two small numbers first, e.g. 2 and 3
Your child can then count in 2s and 3s to get to 6.
Do this a couple of times and then do the same with 3 nos, e.g. 2, 3 and 4.

You are singing my song, good to see that someone else thinks with the same perceptive insight. Certainly, I wouldn't "faff around" with strips of paper.

[russet]

It depends on what suits the child. Some don't get on with numbers as much as they like playing with patterns. One of the good things about using coloured squares is you can then see the patterns. You can also ask what would happen if they did not line up at the beginning. You could just tick squares on a graph sheet if you did not want to cut out. Maths should be about playing and exploring patterns and any way you can get a child to do that the better.

[moved]

I love the strips idea. Out with the Cuisenaire Rods again.