Box M and Box N are identical. ⁶₇ of Box M and ²₅ of Box N are filled with sand. The mass of Box N with its contents is ⁹₁₀ the mass of Box M with its contents. The total mass of the two boxes with their contents is 304 kg. Find the mass of an empty box.
Mass of Box M and its contents = 10 u
Mass of Box N and its contents = 9 u

Total mass of the two boxes with their contents
= 10 u + 9 u
= 19 u

19 u = 304 

1 u = 304 ÷ 19 = 16

Mass of Box M with its concents more than mass of Box N with its contents
= 10 u - 9 u
= 1 u
= 1 x 16
= 16 kg

Fraction of the sand that Box M had more than Box N
= ⁶₇ - ²₅
= ³⁰₃₅ - ¹⁴₃₅
= ¹⁶₃₅

¹⁶₃₅ of the capacity of sand in a box → 16
¹₃₅ of the capacity of sand in a box → 16 ÷ 16 = 1
¹⁴₃₅ of the capacity of sand in a box → 14 x 1 = 14 

Mass of the sand and Box N
= 9 u
= 9 x 16
= 144 kg

Mass of the empty box
= 144 - 14
= 130 kg

Answer(s): 130 kg