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### Number and algebra

### Geometry and measure

### Probability and statistics

### Working mathematically

### For younger learners

### Advanced mathematics

# Stop the Clock for Two

**Notes for adults**

Stop the clock helps to develop children's fluency with telling the time and calculating time intervals. However, the real challenge is to find a winning strategy!

**Easier version:** start at 9 o'clock instead of 6 o'clock.

**Harder version:** try using different time intervals e.g. $\frac{1}{4}$, $\frac{1}{2}$ or $\frac{3}{4}$ hour.

Repeat the game, aiming to find a winning strategy, then talk together about how it was found.

There's a classroom version of this game here.
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### Planet Plex Time

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Links to the University of Cambridge website
Links to the NRICH website Home page

Nurturing young mathematicians: teacher webinars

30 April (Primary), 1 May (Secondary)

30 April (Primary), 1 May (Secondary)

Or search by topic

Age 5 to 7

Challenge Level

- Game

Here's a game to play with an adult!

**How do you play?**

You'll need an adult to play with.

You'll also need a set of blank clock faces, or you could use the interactive version.

Set the time on the clock to 6 o'clock to start the game.

Starting with the adult, take it in turns to move the hands of the clock on by $\frac{1}{2}$ hour or 1 hour. For example, the adult could choose $\frac{1}{2}$ hour, so the clock hands move to 6.30, then you might choose 1 hour, moving the clock hands to 7.30, and so on.

The winner is the person who moves the hands exactly onto 12 o'clock.

Does it make a difference if you go first instead?

What happens if the adult gets to 10.30? Why?

Can you work out a winning strategy?

Stop the clock helps to develop children's fluency with telling the time and calculating time intervals. However, the real challenge is to find a winning strategy!

Repeat the game, aiming to find a winning strategy, then talk together about how it was found.

There's a classroom version of this game here.

On Planet Plex, there are only 6 hours in the day. Can you answer these questions about how Arog the Alien spends his day?

Read this article to find out the mathematical method for working out what day of the week each particular date fell on back as far as 1700.