Box F and Box G are identical. ⁷₈ of Box F and ²₅ of Box G are filled with sand. The mass of Box G with its contents is ⁷₈ the mass of Box F with its contents. The total mass of the two boxes with their contents is 285 kg. Find the mass of an empty box.
Mass of Box F and its contents = 8 u
Mass of Box G and its contents = 7 u

Total mass of the two boxes with their contents
= 8 u + 7 u
= 15 u

15 u = 285 

1 u = 285 ÷ 15 = 19

Mass of Box F with its concents more than mass of Box G with its contents
= 8 u - 7 u
= 1 u
= 1 x 19
= 19 kg

Fraction of the sand that Box F had more than Box G
= ⁷₈ - ²₅
= ³⁵₄₀ - ¹⁶₄₀
= ¹⁹₄₀

¹⁹₄₀ of the capacity of sand in a box → 19
¹₄₀ of the capacity of sand in a box → 19 ÷ 19 = 1
¹⁶₄₀ of the capacity of sand in a box → 16 x 1 = 16 

Mass of the sand and Box G
= 7 u
= 7 x 19
= 133 kg

Mass of the empty box
= 133 - 16
= 117 kg

Answer(s): 117 kg