Two identical containers W and X contained some water. Container W was ¹₇ filled and Container X was ¹₈ filled. The ratio of the total mass of Container W and the water in it to the total mass of Container X and the water in it was 12 : 11. The total mass of the two containers and the water they contained was 3910 g. What is the mass of an empty container?
Mass of Container W and the water inside = 12 u
Mass of Container X and the water inside = 11 u

Total mass of the two containers and the water inside them
= 12 u + 11 u
= 23 u

23 u = 3910

1 u = 3910 ÷ 23 = 170

Mass of Container W and the water in it more than mass of Container X and the water in it 
= 12 u - 11 u
= 1 u

Fraction of the water that Container W had more than Container X 
= ¹₇ - ¹₈
= ⁸₅₆ - ⁷₅₆
= ¹₅₆ 

¹₅₆ of the water capacity → 1 u
⁷₅₆ of the water capacity → 7 x 1 u = 7 u

Mass of an empty container
= 11 u - 7 u
= 4 u
= 4 x 170
= 680 g

Answer(s): 680 g