Delhi Police Constable Exam Model Paper 3

Concept Used:

Where,
n= number of small triangles
H = number of ‘end to end’ horizontal lines
→ In, ∆ABC:

n= number of small triangles = 3
H = number of ‘end to end’ horizontal lines = 1 (BC,)
Triangles = $3\times \frac{3+1}{2}\times 1=6$
Hence, Total triangles in ∆ABC = 6
→Now Adding all the ∆s:
Total ∆s = 12 + 6 = 18
Hence, the correct answer is 18.