Using multiples

Here is an example of a word-based question in maths:

quote
Brian, a lighthouse keeper, switches on the lighthouse light at exactly 9pm. The light rotates in such a way that it looks like it flashes every 8 seconds. This means the first flash appears 8 seconds after 9pm. Susan gets up out of her chair at 9pm, puts the kettle on and looks out of her window at the lighthouse. The time it takes her to reach the window is 57 seconds. If she looks out for 5 seconds, will she see the light flash?

Word-based questions can be long! To help answer this kind of question:

1. Highlight the key information:

Brian, a lighthouse keeper, switches on the lighthouse light at exactly 9pm. The light rotates in such a way that it looks like it flashes every 8 seconds. This means the first flash appears 8 seconds after 9pm. Susan gets up out of her chair at 9pm, puts the kettle on and looks out of her window at the lighthouse. The time it takes her to reach the window is 57 seconds. If she looks out for 5 seconds, will she see the light flash?

This problem involves multiples. The lighthouse flashes every 8 seconds, so the times it flashes are all multiples of 8.

2. Organise the key information:

LighthouseSusan
Starts at 9pm - flashes every 8 secondsStarts at 9pm - gets to window after 57 seconds. Stays there for 5 more seconds.
First flash at 8 secondsArrives at the window at 57 seconds
Next flash at 16 secondsIs at the window at 58 seconds
Next flash at 24 secondsIs at the window at 59 seconds
Next flash at 32 secondsIs at the window at 60 seconds
Next flash at 40 secondsIs at the window at 61 seconds
Next flash at 48 secondsIs at the window at 62 seconds
Next flash at 56 secondsShe stops looking out of the window
Next flash at 64 seconds
Next flash at 72 seconds

3. Use that information to work out the answer to the question:

Question

Will Susan see the lighthouse light flash?

The lighthouse flashed at 56 seconds and then next at 64 seconds.

Susan was only looking out of the window at the lighthouse for 5 seconds in total, between 57 and 62 seconds.

This means the answer is: Susan did not see the light flash.

curriculum-key-fact
It is good practice to answer word-based questions in full sentences.