A cuboid has dimensions [tex]\( x \, \text{cm}, x \, \text{cm}, \)[/tex] and [tex]\( y \, \text{cm} \)[/tex].

- [tex]\( x \)[/tex] is increased by [tex]\( 20\% \)[/tex].
- [tex]\( y \)[/tex] is decreased by [tex]\( 10\% \)[/tex].

Work out and describe the percentage change in the volume of the cuboid. [4 marks]



Answer :

To determine the percentage change in the volume of the cuboid given the changes in its dimensions, let's follow the steps systematically.

1. Initial Dimensions:
- The initial dimensions of the cuboid are [tex]\(x \text{ cm}\)[/tex], [tex]\(x \text{ cm}\)[/tex], and [tex]\(y \text{ cm}\)[/tex].

2. Initial Volume Calculation:
- The initial volume of the cuboid can be calculated using the formula for the volume of a cuboid:
[tex]\[ \text{Volume}_{\text{initial}} = x \cdot x \cdot y = x^2 \cdot y \][/tex]
- Assume initial values of [tex]\(x = 1 \text{ cm}\)[/tex] and [tex]\(y = 1 \text{ cm}\)[/tex] for simplicity.
[tex]\[ \text{Volume}_{\text{initial}} = 1 \cdot 1 \cdot 1 = 1 \text{ cm}^3 \][/tex]

3. Changes in Dimensions:
- [tex]\(x\)[/tex] is increased by [tex]\(20\%\)[/tex]:
[tex]\[ \text{New } x = x \cdot (1 + 0.2) = 1 \cdot 1.2 = 1.2 \text{ cm} \][/tex]

- [tex]\(y\)[/tex] is decreased by [tex]\(10\%\)[/tex]:
[tex]\[ \text{New } y = y \cdot (1 - 0.1) = 1 \cdot 0.9 = 0.9 \text{ cm} \][/tex]

4. New Volume Calculation:
- With the new dimensions, the new volume of the cuboid is:
[tex]\[ \text{Volume}_{\text{new}} = \text{New } x \cdot \text{New } x \cdot \text{New } y = 1.2 \cdot 1.2 \cdot 0.9 \][/tex]
- Simplifying this,
[tex]\[ \text{Volume}_{\text{new}} = 1.44 \cdot 0.9 = 1.296 \text{ cm}^3 \][/tex]

5. Percentage Change in Volume:
- To find the percentage change in volume, we use the formula for percentage change:
[tex]\[ \text{Percentage Change} = \frac{\text{New Volume} - \text{Initial Volume}}{\text{Initial Volume}} \times 100\% \][/tex]
- Substituting the values we calculated,
[tex]\[ \text{Percentage Change} = \frac{1.296 \text{ cm}^3 - 1 \text{ cm}^3}{1 \text{ cm}^3} \times 100\% \][/tex]
[tex]\[ \text{Percentage Change} = \frac{0.296 \text{ cm}^3}{1 \text{ cm}^3} \times 100\% = 29.6\% \][/tex]

Therefore, the percentage change in the volume of the cuboid, given the changes in its dimensions, is a 29.6% increase.