How many cubes with an edge of 2 cm can be fitted into a box of dimension $8 cm\times 5 cm\times 4 cm$.

Given : edge of a cube = 2 cm

             dimension of box = $8 cm\times 5 cm\times 4 cm$

To find: the number of cubes that can be fitted in the box

Solution: 

Volume of box $=l\times b\times h=8\times 5\times 4=160 c{m}^3$

Volume of cube $=a^3=2\times 2\times 2=8 c{m}^3$

No. of cubes that can be fitted in the box = $\frac{volume of box}{volume of cube}=\frac{160 c{m}^3}{8 c{m}^3}$

Therefore, the required number of cubes that can be fitted in the box is 20.

Hence, the correct option is D