Question

The 20th term in the triangular numbers 1, 3, 6, 10, 15, 21, ... is

• A. 190
• B. 195
• C. 200
• D. 210

Hint:

Remember triangular number formula: $\frac{n(n+1)}{2}$.

Answer 1

The Correct Option is D

Concept: Triangular number formula: \[ T_n = \frac{n(n+1)}{2} \] Explanation: For $n = 20$: \[ T_{20} = \frac{20 \times 21}{2} = 210 \]