You are given an equilateral triangle of three matchsticks like given figure. What is the minimum number of sticks needed to add three more equilateral triangles to it?
Answer : 3
Explanation : Technically 4 triangles require 12 matchsticks, but we only have 6, that means each matchstick must be used in 2 triangles. So every triangle has to border 3 other triangles (one on each side).It’s a tetrahedron (a three-sided pyramid).
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