The marked choices are correct.
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1. The number of sides decreases from 7 to 6 to 5 to 4. We expect the next number of sides to be 3. A triangle has 3 sides.
2. Each number is half the previous one. We expect the next number to be half of -6, which is -3.
3. The figure number is the number of non-overlapping triangles. The 20th figure will have 20 triangles. The number of distinct line segments in 20 non-overlapping triangles is 20·3 = 60.
