Question

Without adding, find the sum of the following:

i.1+3+5+7+9+11+13+15+17+19+21 =___

Answer 1

Sum of n consecutive odd integers starting from 1 is equal to $n^2$, where 'n' is the number of terms involved in the series.
Therefore,
i. 1+3+5+7+9+11+13+15+17+19+21 = sum of first 11 odd integers = ${11}^2=121$.