Two identical pails D and E contained some water. Pail D was ¹₂ filled and Pail E was ¹₃ filled. The ratio of the total mass of Pail D and the water in it to the total mass of Pail E and the water in it was 5 : 4. The total mass of the two pails and the water they contained was 1260 g. What is the mass of an empty pail?
Mass of Pail D and the water inside = 5 u
Mass of Pail E and the water inside = 4 u

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

9 u = 1260

1 u = 1260 ÷ 9 = 140

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

Fraction of the water that Pail D had more than Pail E 
= 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 pail
= 4 u - 2 u
= 2 u
= 2 x 140
= 280 g

Answer(s): 280 g