The value of 1 + 3 + 5 + 7 + …… + 21 =

Correct option is A

Given:  

$$1 + 3 + 5 + 7 + \dots + 21$$​​

Formula Used:

Sum of n terms of an arithmetic series:

$$S_n = \frac{n}{2} \cdot (a + l)$$​​

Solution: ​

First term a = 1 ,

Common difference d= 2, 

Last term l = 21

number of terms :

$$n = \frac{21 - 1}{2} + 1 = 11 \\ \ \\ \text{ Putting the values in the formula} :$$

$$S_n = \frac{11}{2} \times (1 + 21) = \frac{11}{2} \times 22 = 11 \times 11 = 121$$