Two identical containers K and L contained some water. Container K was ¹₂ filled and Container L was ¹₃ filled. The ratio of the total mass of Container K and the water in it to the total mass of Container L and the water in it was 7 : 6. The total mass of the two containers and the water they contained was 2730 g. What is the mass of an empty container?
Mass of Container K and the water inside = 7 u
Mass of Container L and the water inside = 6 u

Total mass of the two containers and the water inside them
= 7 u + 6 u
= 13 u

13 u = 2730

1 u = 2730 ÷ 13 = 210

Mass of Container K and the water in it more than mass of Container L and the water in it 
= 7 u - 6 u
= 1 u

Fraction of the water that Container K had more than Container L 
= ¹₂ - ¹₃
= ³₆ - ²₆
= ¹₆ 

¹₆ of the water capacity → 1 u
²₆ of the water capacity → 2 x 1 u = 2 u

Mass of an empty container
= 6 u - 2 u
= 4 u
= 4 x 210
= 840 g

Answer(s): 840 g