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Find the fifth triangular number.
Triangular number:
A triangular number counts objects arranged in an equilateral triangle.
$n^{th}$ triangular number is given by $\frac{n(n+1)}{2}$.
Fifth triangular number $= \frac{5(5+1)}{2} = \frac{5\times 6}{2} = 5\times3 = 15$.
Therefore, the fifth triangular number is 15.
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