Question

Observe the figures and predict the number of dots in next figure?

• A. $25$
• B. $20$
• C. $21$
• D. $30$

Answer 1

The correct option is C $21$

The answer is option $C$

The pattern followed is:

$1+2$
$1+2+3$
$1+2+3+4$ and so on
In terms of number of layers the formula for this pattern is

$\frac{(N+1)(N+2)}{2}$, where $N$ is the number of layers below the vertex.

In the final figure, where there will be $5$ layers, the number of dots $=\frac{6\times 7}{2}=21$