Welcome back. 

This week we are going to start looking at multiples, factors and prime numbers. What can you remember about these?

Have a look at the following problem.

What would be the best way to record the train arrival times so it is possible to compare the times for both trains. Would a table be useful?

My friend says that if the trains both start at 4 p.m., they won't meet up again because 20 minutes is even and 15 minutes is odd. Is this correct? How can we tell? 

 Now look at the following table. 

From the table of arrival times, we can see that the trains arrive at the same time on the hour. Why is that so? Is it possible to calculate that using mathematics?

That's right, you can list the multiples of 15 and 20.

To calculate the times when the trains will arrive at the same time, we just need to find the common multiple. Remember that common multiples are the ones in both lists.

 So we now know that 60 is a common multiple of 15 and 20. We know there are 60 minutes in 1 hour so we can use this knowledge to predict that the trains will arrive at the same time every hour.

Now have a go at the guided practice. If you are at home, record this in your home books. Remember to present your work neatly so you can compare your lists.