What happens to the perimeter of triangle ABC as the two smaller
circles change size and roll around inside the bigger circle?
Two semicircle sit on the diameter of a semicircle centre O of
twice their radius. Lines through O divide the perimeter into two
parts. What can you say about the lengths of these two parts?
A point P is selected anywhere inside an equilateral triangle. What
can you say about the sum of the perpendicular distances from P to
the sides of the triangle? Can you prove your conjecture?
This problem encourages students to think about the properties of numbers. It could be used to consolidate work on linear sequences. The interactivity encourages learners to begin the problem experimentally before working more theoretically as they engage with the main ideas.
What is true about any pair of rules where it is not possible to light up both lights?
If two sequences are described by the rules $an+b$ and $cn+d$, can you explain the conditions for determining whether the lights will ever switch on together?
Some students may wish to use ideas of modular arithmetic to prove their findings; reading this article first may help.
The problem Shifting Times Tables offers an introductory challenge for exploring linear sequences.
In the Hint there is a version of the interactivity with just two lights which students might find more accessible.
Students could use a 100 square (Word, pdf) as a visual way to record sequences and see where (if) they coincide.