You may also like

problem icon


Which times on a digital clock have a line of symmetry? Which look the same upside-down? You might like to try this investigation and find out!

problem icon

Clock Hands

This investigation explores using different shapes as the hands of the clock. What things occur as the the hands move.

problem icon

Ten Green Bottles

Do you know the rhyme about ten green bottles hanging on a wall? If the first bottle fell at ten past five and the others fell down at 5 minute intervals, what time would the last bottle fall down?

Take the Right Angle

Stage: 2 Challenge Level: Challenge Level:1

Take the Right Angle

How many times in twelve hours do the hands of a clock form a right angle? Use the + and - buttons below to move the hands of the NRICH clock, then click on the right angle symbol to check your answer.
If you can see this message Flash may not be working in your browser
Please see to enable it.
What are these times to the nearest minute?

Why do this problem?

This problem is one which could be done as an introduction when extending or revising work on time and clocks. It will encourage the use of digital times.

Key questions

At what time is the first right angle after $12$ o'clock?

Why is it not just $15$ minutes later?

Can you write down these times using digital notation?

Why is the number of times not divisible by $4$?

Possible extension

Learners could find out the times for $24$ hours and record using $24$ hour digital notation.

Possible support

Suggest counting round a clock, or using the interactive clock in the question.