How many planks of dimensions (5 m × 25 cm × 10 cm) can be stored in a pit which is 20 m long,

Number of planks $=\frac{\text { volume of the pit in } \mathrm{cm}^{3}}{\text { volume of } 1 \text { plank in } \mathrm{cm}^{3}}$

Volume of one plank $=(l \times b \times h) \mathrm{cm}^{3}$

$=500 \times 25 \times 10 \mathrm{~cm}^{3}$

$=125000 \mathrm{~cm}^{3}$

Volume of the pit $=(l \times b \times h) \mathrm{cm}^{3}$

Here, $l=20 \mathrm{~m}=2000 \mathrm{~cm} ; b=6 \mathrm{~m}=600 \mathrm{~cm} ; h=80 \mathrm{~cm}$

i.e., volume of the pit $=2000 \times 600 \times 80 \mathrm{~cm}^{3}$

$=96000000 \mathrm{~cm}^{3}$

$\therefore$ Number of planks $=\frac{96000000}{125000}=\frac{96000}{125}=768$