A pattern of dots forms triangular numbers: Figure 1 has 1 dot, Figure 2 has 3 dots, Figure 3 has 6 dots, Figure 4 has 10 dots. The number of dots in Figure n follows the formula n × (n + 1) ÷ 2. Find the number of dots in Figure 12.
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Worked Solution
Step 1: Use the formula: dots = n × (n + 1) ÷ 2.
Step 2: For Figure 12: 12 × 13 ÷ 2 = 156 ÷ 2 = 78.
Answer: 78
Correct answer: 78
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