Answer:
20
Explanation:
The number of combinations of 6 points taken 3 at a time is ...
6!/(3!·(6-3)!) = 6·5·4/(3·2·1) = 5·4 = 20
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If you number the points 1–6, the points of the 20 triangles will be ...
123 124 125 126 134
135 136 145 146 156
234 235 236 245 246
256 345 346 356 456