Two identical containers E and F contained some water. Container E was ¹₂ filled and Container F was ¹₃ filled. The ratio of the total mass of Container E and the water in it to the total mass of Container F and the water in it was 5 : 4. The total mass of the two containers and the water they contained was 1980 g. What is the mass of an empty container?
Mass of Container E and the water inside = 5 u
Mass of Container F and the water inside = 4 u

Total mass of the two containers and the water inside them
= 5 u + 4 u
= 9 u

9 u = 1980

1 u = 1980 ÷ 9 = 220

Mass of Container E and the water in it more than mass of Container F and the water in it 
= 5 u - 4 u
= 1 u

Fraction of the water that Container E had more than Container F 
= 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
= 4 u - 2 u
= 2 u
= 2 x 220
= 440 g

Answer(s): 440 g