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Triangle Incircle Iteration

Keep constructing triangles in the incircle of the previous triangle. What happens?

Vedic Sutra - All from 9 and Last from 10

Vedic Sutra is one of many ancient Indian sutras which involves a cross subtraction method. Can you give a good explanation of WHY it works?

Tournament Scheduling

Scheduling games is a little more challenging than one might desire. Here are some tournament formats that sport schedulers use.

Zeller's Birthday

Age 14 to 16
Challenge Level

The calculation must 'count back', or 'count forward', from somewhere in some way.

First in whole weeks, then the bit that is left (the days that don't make a whole week) could indicate the position in the week, ie. 'day'
The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice.
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