alleryDots form triangles with 1, 3, 6, 10, 15 dots. How many dots in the next?
A28
B21
C24
D20
Answer & Solution
Correct answer: B. 21
The gaps grow by one each time (2, 3, 4, 5), so the next gap is 6 and 15 + 6 = 21.
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