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Four vehicles travelled on a road. What can you deduce from the times that they met?

### There and Back

Brian swims at twice the speed that a river is flowing, downstream from one moored boat to another and back again, taking 12 minutes altogether. How long would it have taken him in still water?

### Escalator

At Holborn underground station there is a very long escalator. Two people are in a hurry and so climb the escalator as it is moving upwards, thus adding their speed to that of the moving steps. ... How many steps are there on the escalator?

# Swimmers

##### Stage: 4 Challenge Level:

Two friends, Alan and Brian, dive in simultaneously from opposite ends of a non-standard swimming pool and swim at constant, but different, speeds.

If they first cross at a distance 30m from Alan's starting end and next cross at a distance 20m from Brian's starting end, how long is this particular pool and where will they next cross ?

Can you generalise this finding?

There are two types of crossing : head-on, as in the illustration, and overtaking. You might need to consider these separately.