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The problem is how did Archimedes calculate the lengths of the sides of the polygons which needed him to be able to calculate square roots?

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?

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'