Question

Observe the dots arranged in triangles. How many dots will be there in the fifth triangle?

• A. $12$
• B. $15$
• C. $18$
• D. $21$

Answer 1

The correct option is B

$15$

We can observe that the number of dots in the triangular figure is as follows

1, 3, 6 ..... and so on

First number is $1$

Second number is $1+2=3$

Third number is $1+2+3=6$

Similarly, fifth number will be

$1+2+3+4+5=15$

Hence, the next triangle will have 15 dots.