The length of a diagonal of a cuboid is 11 cm. The surface area is 240 square cm. What is the sum of its length, breadth and height ? 

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CDS Elementary Mathematics 16 April 2023 Official Paper
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  1. 16 cm
  2. 17 cm 
  3. 18 cm 
  4. 19 cm 

Answer (Detailed Solution Below)

Option 4 : 19 cm 
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Detailed Solution

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Formula used:

The diagonal of a cuboid is given by: √(L² + B² + H²)

The surface area of a cuboid is given by: 2(LB + BH + HL) 

(a + b + c)² = a² + b² + c² + 2(ab + bc + ac)

Calculation:

By using the above formula

√(L² + B² + H²) = 11 cm

2(LB + BH + HL) = 240cm²

⇒ LB + BH + HL = 120cm²

We know that

(a + b + c)² = a² + b² + c² + 2(ab + bc + ac)

(L + B + H)² = 11² + 2 × 120 = 121 + 240 = 361

Taking the square root of both sides 

∴ L + B + H = √361 = 19cm

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