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The volume of a cube is \(8\text{ cm}^3\) and is equal to the volume of a cuboid of length x, breadth y and height z, where x, y and z are natural numbers \((x > y > z)\). Let n be the number of such cuboids with different dimensions. What is the value of n ?

This question was previously asked in
CDS 1 2026 Maths Question Paper (12-Apr-2026)
The correct answer is

1

To solve this problem, we need to determine the number of cuboids with distinct dimensions whose volume equals the volume of a cube with sides measuring \(2 \, \text{cm}\) (since \(2^3 = 8 \, \text{cm}^3\)).

Given: The volume of the cube is \(8 \, \text{cm}^3\). The formula to calculate this is:

\(V_{\text{cube}} = a^3 = 8\), where \(a\) is the side of the cube.

Solving for \(a\), we find:

\(a = \sqrt[3]{8} = 2\)

Thus, the side of the cube is \(2 \, \text{cm}\).

Now, consider the cuboid with dimensions \(x, y, z\), where the volume is given as:

\(V_{\text{cuboid}} = x \cdot y \cdot z = 8\)

We are given the condition \(x > y > z\) and that \(x, y, z\) are natural numbers. We will check every set of numbers that multiply to \(8\):

  • If \(z = 1\), then \(x \cdot y = 8\). Checking integer pairs, possible solutions are:
    • \(y = 2, x = 4\), leading to the triplet \((4, 2, 1)\). This satisfies \(x > y > z\).
    • Any other combinations such as \(y = 4, x = 2\) don't satisfy the condition \(x > y > z\).
  • If \(z = 2\), then \(x \cdot y = 4\). Checking integer pairs for \(y\) and \(x\) doesn't provide additional solutions since \({2, 1}\) already uses these factors and the only valid order found is \({4, 2, 1}\).

Hence, only one valid set of natural number dimensions satisfies all the conditions: \((4, 2, 1)\).

The number of distinct cuboids is 1.

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