alleryWhat is the 10th triangular number?
A100
B45
C55
D50
Answer & Solution
Correct answer: C. 55
1. The nth triangular number is 1 + 2 + ... + n.
2. 1 + 2 + ... + 10 = 10 x 11 / 2.
3. 110 / 2 = 55.
_Source: Wikipedia, Triangular number (CC BY-SA 4.0), Triangular number_
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