Two identical containers B and C contained some water. Container B was ¹₈ filled and Container C was ¹₉ filled. The ratio of the total mass of Container B and the water in it to the total mass of Container C and the water in it was 11 : 10. The total mass of the two containers and the water they contained was 4620 g. What is the mass of an empty container?
Mass of Container B and the water inside = 11 u
Mass of Container C and the water inside = 10 u

Total mass of the two containers and the water inside them
= 11 u + 10 u
= 21 u

21 u = 4620

1 u = 4620 ÷ 21 = 220

Mass of Container B and the water in it more than mass of Container C and the water in it 
= 11 u - 10 u
= 1 u

Fraction of the water that Container B had more than Container C 
= 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
= 10 u - 8 u
= 2 u
= 2 x 220
= 440 g

Answer(s): 440 g