Question

The tenth triangular number is ___.

• A. 55
• B. 45
• C. 36
• D. 60

Answer 1

The correct option is A

55

The $n^{th}$ triangular numbers can be obtained using the formula $\frac{n(n+1)}{2}.$

Substituting n = 10 we get

${10}^{th}$ triangular number = $\frac{10\left(11\right)}{2}$

= 55