Q4 of 16 Page 53

Debnath has made a cuboid whose length, breadth and height are 4 cm, 3 cm and 2 cm respectively. Let’s see how many cuboids of this type will form a cube.

Given that,

Debnath made a cuboid of dimension:


Length = 4 cm


Breadth = 3 cm


Height = 2 cm


Since, volume of cuboid = length × breadth × height


Volume of cuboid = 4 × 3 × 2


= 24


Therefore, volume of a cuboid made by Debnath is 24 cm3.


Factors of 24 are:


24 = 2 × 2 × 2 × 3


This 24 cm3 is volume of one cuboid, which is not even perfect cube.


And to form a cube, we need to have perfect cube volumes.


So make 24 into a perfect cube.


Notice the factors of 24,


24 = 2 × 2 × 2 × 3


Group three similar integers, we get


24 = (2 × 2 × 2) × 3


Multiply both sides by (3 × 3), we get


24 × (3 × 3) = (2 × 2 × 2) × 3 × (3 × 3)


216 = (2 × 2 × 2) × (3 × 3 × 3)


Number of cuboids = (3 × 3)


Because multiplying (3 × 3) makes a cube by the same number of cuboids.


Number of cuboids = 9


Thus, number of required cuboids are 9.


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