A cuboidal box has dimensions $1.2$ m $\times 0.8$ m $\times 0.5$ m. The cost of painting all its faces at…

A cuboidal box has dimensions $1.2$ m $\times 0.8$ m $\times 0.5$ m. The cost of painting all its faces at $\text{Rs.}\,50$ per m$^{2}$ is:
  1. $\text{Rs.}\,196$
  2. $\text{Rs.}\,98$
  3. $\text{Rs.}\,392$
  4. $\text{Rs.}\,240$

Solution

TSA $= 2(1.2 \cdot 0.8 + 0.8 \cdot 0.5 + 0.5 \cdot 1.2) = 2(0.96+0.40+0.60) = 2 \times 1.96 = 3.92 \text{ m}^{2}$. Cost $= 3.92 \times 50 = \text{Rs.}\,196$.

Asked in: IMO

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