May Challenge - Years 3 & 4

Lighthouses

On the coast there are three lighthouses.

The first light shines for 3 seconds, then is off for 3 seconds.

The second light shines for 4 seconds, then is off for 4 seconds.

The third light shines for 5 seconds, then is off for 5 seconds.

All three lights have just come on together.

Questions:

1) When is the first time that all three lights will be off?

2) When is the next time that all three lights will come on at the same moment?

Hints:
Think about drawing three number lines (one for each lighthouse) to show when each light is on and off.  Be sure to match the three lines up so they are easy to compare.
Question 2 will require some careful work and perseverance if you use the number lines.  Alternatively, you may wish to think about the number of seconds between each turning on of  a light.  For example, the first lighthouse turns on every 6 seconds.  Think about how you could use your knowledge of multiples.

Solutions are to be completed by Thursday 26^th May.  Please post them into the Maths Challenge Box in the picture book library.