I have a question regarding R.D sharma .
In pg 18.14, ex 18.1, why is it while finding the inner dimensions we have to subtract twice the thickness.

Dear Student,
Please find below the solution to the asked query :

Suppose the external dimension of an open box are : 148 cm $\times$ 116 cm $\times$ 83 cm. It is made up of 3 cm thick wood.
Now, we have to find the inner dimensions of the box.



  

$$\begin{gathered} \mathrm{We} \mathrm{have},\mathrm{outer} \mathrm{length} = 148 \mathrm{cm} \\ \mathrm{Now}, \mathrm{inner} \mathrm{length} = 148 - 3 - 3 = 142 \mathrm{cm} \\ \mathrm{Outer} \mathrm{breadth} = 116 \mathrm{cm} \\ \mathrm{inner} \mathrm{breadth} = 116 - 3 - 3 = 110 \mathrm{cm} \\ \mathrm{outer} \mathrm{height} = 83 \mathrm{cm} \\ \mathrm{Inner} \mathrm{height} = 83 - 3 =80 \mathrm{cm} \left(\mathrm{as} \mathrm{the} \mathrm{box} \mathrm{is} \mathrm{open}\right) \end{gathered}$$


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