A big triangle has four lines drawn from one corner to the opposite side, splitting it into five thin triangles. How many triangles of all sizes are there?
Answer and explanation
Correct answer: C. 15
- Step 1: Each triangle has two of the six points along the base as its bottom corners, with the top corner shared.
- Step 2: Pairs of points from six: 6 x 5 / 2 = 15 triangles.
Answer
15.
Why not the others: 5 counts only the thin triangles, 10 uses only five points on the base and 20 over-counts.
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