Light P flashes every 12 seconds.
Light Q flashes every 15 seconds.
Light R flashes every 18 seconds.
All three lights flash at the same time.
Work out how long it will take for all three lights to flash at the same time again.
59 exam-style questions on Edexcel GCSE Maths Prime Factors, HCF and LCM. Each one has a worked solution and a mark scheme showing where the marks go.