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### Question

What is the average of first 275 natural numbers?

**A**

138.

**B**

139.

**C**

137.

**D**

136.

**Soln.**

**Ans: a**

The sum of first n natural numbers is $(n × (n + 1))/2$. The average is ${(n × (n + 1))/2}/n$ which is $(n + 1)/2.$ Putting n = 275, we get average = 138.