Comprehension

The perimeter of a triangle ABC is 105 cm. The altitudes AD, BE and CF are in the ratio 3 : 5 : 6.

What is the approximate area of the triangle ABC?

This question was previously asked in
UPSC CDS-I 2025 (Elementary Mathematics) Official Paper (Held On: 13 Apr, 2025)
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  1. 175 square cm
  2. 190 square cm
  3. 205 square cm
  4. 285 square cm

Answer (Detailed Solution Below)

Option 4 : 285 square cm
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Detailed Solution

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Given:

Perimeter of triangle ABC = 105 cm

Ratio of sides AB : BC : CA = 5 : 10 : 6

Formula used:

Heron's Formula for the area of a triangle:

Area =

Where a, b, c are the lengths of the sides of the triangle, and

s is the semi-perimeter s =

Calculations:

From the previous problem, we established

The ratio of the sides AB : BC : CA = 5 : 10 : 6.

Let the sides be AB = 5x, BC = 10x, and CA = 6x.

The perimeter is the sum of the sides:

Perimeter = AB + BC + CA = 5x + 10x + 6x = 21x

Given Perimeter = 105 cm.

⇒ 21x = 105

⇒ x =

⇒ x = 5

a (BC) = 10x = 10 × 5 = 50 cm

b (CA) = 6x = 6 × 5 = 30 cm

c (AB) = 5x = 5 × 5 = 25 cm

The semi-perimeter (s): s = = = 52.5 cm

Area =

Area =

Area =

Area =

Area ≈ 284.975 cm2

Area ≈ 285 cm2

∴ The correct answer is option 4.

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