Correct option is (b) \(\frac 1{21} \)kg, \(\frac 19\)kg
Dimension of a closed rectangular wooden box are 18cm,10cm and 6cm, respectively.
The thickness of wood is 21cm
∴ Volume of rectangular wooden block = 18 × 10 × 6 = 1080 cm3
And, volume of hollow space in rectangular wooden block = 17 × 9 × 5 = 765 cm3
∴ Volume of rectangular wood = (1080 − 765)cm3 = 365 cm3
Now, weight of empty box = 15kg
∴ Weight of a cubic cm of wood = \(\frac{15}{365}\) = \(\frac 1{21}\) kg
Weight of box filled with sand = 100kg
Weight of sand = (100 − 15)kg = 85kg
∴ Weight of a cubic cm of sand = \(\frac{85}{765}\) kg = \(\frac 19\)kg