Question

What is the ${89}^{th}$ term in the given sequence? 1,3,6,10,15 .............

• A. 5005
• B. 5185
• C. 4005
• D. 4785

Answer 1

The correct option is C

4005

In the given sequence $n^{th}$ term is the sum of the first n natural numbers.

${89}^{th}$ term is the sum of the first 89 natural numbers.

The natural numbers form an A.P. with the first term as 1 and common difference as 1.

Sum of 89 natural numbers $=\frac{89}{2}(2+(89-1\left)\right)$
=4005