With two problems counting triangles in the international exam for 6th-7th graders, how long can you solve them?
Lesson 1 (Excerpt from APMOPS 2005 Math Olympiad exam):
Given 12 points on 2 lines (a),(b) as shown below. Ask how many triangles have 3 vertices taken from 3 of the 12 given points.
Lesson 2 (Excerpt from BIMC 2013 Math Olympiad entrance exam):
Given 21 points on 3 lines (a),(b),(c) as shown below. Ask how many triangles with 3 vertices taken from 3 of the 21 given points are there at most.
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Tran Phuong
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