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Question

The cost of painting a cube on all the external surfaces at the rate of ₹2/cm$^2$ is ₹588. Find the volume of the cube (in cm$^3$).

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
343

Cube Volume Calculation from Painting Cost

The problem asks for the volume of a cube, given the total cost of painting all its external surfaces and the painting rate.

Step 1: Calculate the Total Surface Area (TSA)

First, find the total surface area that was painted. This is done by dividing the total cost by the rate per square centimeter.

  • Total Cost = ₹588
  • Rate = ₹2/cm$^2$
  • Total Surface Area (TSA) = $\frac{\text{Total Cost}}{\text{Rate}}$

    TSA = $\frac{₹588}{₹2/\text{cm}^2}$ = 294 cm$^2$

Step 2: Determine the Side Length of the Cube

The formula for the total surface area of a cube with side length '$a$' is $6a^2$. We use the TSA calculated in Step 1 to find '$a$'.

  • TSA = $6a^2$
  • $294 \text{ cm}^2 = 6a^2$
  • $a^2 = \frac{294 \text{ cm}^2}{6}$
  • $a^2 = 49 \text{ cm}^2$
  • $a = \sqrt{49 \text{ cm}^2}$
  • $a = 7 \text{ cm}$

Step 3: Calculate the Volume of the Cube

Finally, calculate the volume of the cube using the side length '$a$' found in Step 2. The formula for the volume (V) of a cube is $a^3$.

  • Volume (V) = $a^3$
  • V = $(7 \text{ cm})^3$
  • V = $7 \times 7 \times 7$ cm$^3$
  • V = 343 cm$^3$

The volume of the cube is 343 cm$^3$. This matches option B.

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