1. Using this picture we can observe that
$$
1+3+5+7=4 \times 4 \text {. }
$$

What is the value of
$$
1+3+5+7+9+11+13+15+17+19+21 ?
$$
1. 121 The sum $1+3+5+7+9+11+13+15+17+19+21$ has eleven terms. Therefore the value of the required sum is $11 \times 11=121$.