The mass of a box completely filled with sand is 9kg. If 1/3 of the sand is poured out, the mass of the box and the remaining sand is 6.1kg. What is the mass of the empty box?
A. 0.2kg
B. 0.3kg
C. 0.4kg
D. 0.5kg
Let's assume the mass of the empty box is "x" kg.
If the mass of a completely filled box is 9kg, and the mass of the empty box is "x" kg, then the mass of the sand in the box is (9-x) kg.
If 1/3 of the sand is poured out, the remaining sand would be (2/3)*(9-x) kg.
If the mass of the box and the remaining sand is 6.1kg, we can set up the equation:
x + (2/3)*(9-x) = 6.1
Multiplying by 3 to remove the fraction:
3x + 2(9-x) = 18.3
Simplifying:
3x + 18 - 2x = 18.3
x + 18 = 18.3
x = 0.3
The mass of the empty box is 0.3kg.
Therefore, the answer is B. 0.3kg.