Question

1+3+5+7+9+11+13+15+17+19+21 without adding

Answer 1

Answer:

121

Step-by-step explanation:

It's a series of odd numbers. Let

$S _{11} = 1+3+5+7+9+11+13+15+17+19+21$

As a rule of thumb, the sum of n numbers of odd numbers is equal to n². There're 11 numbers in this series. Hence The sum is 11² =121

Answer 2

Answer:

121

Step-by-step explanation:

1 + 3 + 5 + 7 + 9 + 11 +  13 + 15 + 17 + 19 + 21 is a sum of first 11 odd numbers.

   $\sf \boxed{\text{\bf Sum of first n odd numbers = n^2 }}$

Here, n is the number of terms.

In this sequence, there are 11 terms.

Sum of first 11 odd numbers = 11²

                                              = 11 *11

                                              = 121