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.

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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.