alleryThe triangular numbers 1, 3, 6, 10, 15 are followed by?
A20
B21
C25
D18
Answer & Solution
Correct answer: B. 21
1. The gaps grow by 1 each time: 2, 3, 4, 5.
2. The next gap is 6.
3. 15 + 6 = 21.
_Source: Wikipedia, Triangular number (CC BY-SA 4.0), Triangular number_
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