Two identical containers H and J contained some water. Container H was ¹₈ filled and Container J was ¹₉ filled. The ratio of the total mass of Container H and the water in it to the total mass of Container J and the water in it was 13 : 12. The total mass of the two containers and the water they contained was 6750 g. What is the mass of an empty container?
Mass of Container H and the water inside = 13 u
Mass of Container J and the water inside = 12 u

Total mass of the two containers and the water inside them
= 13 u + 12 u
= 25 u

25 u = 6750

1 u = 6750 ÷ 25 = 270

Mass of Container H and the water in it more than mass of Container J and the water in it 
= 13 u - 12 u
= 1 u

Fraction of the water that Container H had more than Container J 
= ¹₈ - ¹₉
= ⁹₇₂ - ⁸₇₂
= ¹₇₂ 

¹₇₂ of the water capacity → 1 u
⁸₇₂ of the water capacity → 8 x 1 u = 8 u

Mass of an empty container
= 12 u - 8 u
= 4 u
= 4 x 270
= 1080 g

Answer(s): 1080 g