Question

In the following, observe the pattern and fill in the blanks.

1 + 3 + 5 = 9
3 + 5 + 7 = 15
5 + 7 + 9 = 21
7 + 9 + 11 = ______
9 + 11+ 13 = ______
15 + 17 + 19 = 51

• A. $27$
• B. $33$

Answer 1

Here, just follow the pattern, in each step the addition of all prime numbers gives the answer.

so

$$\begin{gathered} 1+3+5=9 \\ 3+5+7=15 \\ 5+7+9=21 \\ 7+9+11=\mathbf{27} \\ 9+11+13=\mathbf{33} \\ 15+17+19=51 \end{gathered}$$

Hence, $27$ and $33$ is a required answer.