CTET 2 Math and Science 23 Dec 2021 Paper

Total surface area of cuboid exclude one surface $=2\left(\mathrm{lb}+\mathrm{bh}+\mathrm{lh}\right)-\mathrm{lb}$
$\Rightarrow$ Total surface area of cuboid exclude one surface $=2\left[\left(12\times 8\right)+\left(8\times 4\right)+\left(12\times 4\right)\right]-\left[12\times 8\right]$
$\Rightarrow$ Total surface area of cuboid exclude one surface $=352-96$
$\Rightarrow$ Total surface area of cuboid exclude one surface $=256{\mathrm{cm}}^2$
$\Rightarrow$ Cost of painting $=256\times 50=$ Rs. 12800
$\therefore$ The cost of painting is Rs. 12,800
The correct option is 3 i.e. Rs. 12,800