   Question Answers

# Find the sum of the first 20 natural numbers. Choose the correct option:A. 210B. 220C. 230D. 240  Hint: It is known that the natural number starts from 1. Also, the sum of the first n natural number is given by: $\dfrac{n(n+1)}{2}$.

In the given problem, we have to find the sum of the first 20 natural numbers.
Now the natural number always starts from 1 and that means 1 is the smallest natural number.
Next, the first 20 natural number will be:
1, 2, 3, 4, 5, …….., 19, 20. Here there are 20 terms.

Now we know that the sum of the first n natural number is given by the formula $\dfrac{n(n+1)}{2}$.
Also, n here is the number of terms and that is equal to 20.
$\Rightarrow n=20$
So the sum of first 20 natural number will be given:
\begin{align} & \Rightarrow \dfrac{n(n+1)}{2} \\ & \Rightarrow \dfrac{20(20+1)}{2} \\ & \Rightarrow 10(21) \\ & \Rightarrow 210 \\ \end{align}
So, now the correct option is A) 210.

Note: It is important to keep in mind that zero is not the natural number. Also, the smallest natural number is one. This problem can also be solved by using the sum of n terms of an arithmetic progression formula i.e. $S_n = \dfrac{n}{2} [2a+(n-1)d]$ where first term (a) = 1, common difference (d) =1 and n =20.
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