Yerlan Abenov

November 9, 2026 · 9 min

Why a minus times a minus is a plus

Yerlan drawing a graph on a whiteboard in front of a class.
A teacher's desk covered with graph paper, tea and a compass.

Free · every Sunday

One problem a week

One short problem on Sunday, a hint on Wednesday, the worked answer on Friday. Good for a teenager on their own, or for the two of you over tea.

This week: three friends share a taxi from the airport and one gets out halfway. Who should pay what?

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