Two identical pails R and S contained some water. Pail R was ¹₆ filled and Pail S was ¹₇ filled. The ratio of the total mass of Pail R and the water in it to the total mass of Pail S and the water in it was 12 : 11. The total mass of the two pails and the water they contained was 5520 g. What is the mass of an empty pail?
Mass of Pail R and the water inside = 12 u
Mass of Pail S and the water inside = 11 u

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

23 u = 5520

1 u = 5520 ÷ 23 = 240

Mass of Pail R and the water in it more than mass of Pail S and the water in it 
= 12 u - 11 u
= 1 u

Fraction of the water that Pail R had more than Pail S 
= ¹₆ - ¹₇
= ⁷₄₂ - ⁶₄₂
= ¹₄₂ 

¹₄₂ of the water capacity → 1 u
⁶₄₂ of the water capacity → 6 x 1 u = 6 u

Mass of an empty pail
= 11 u - 6 u
= 5 u
= 5 x 240
= 1200 g

Answer(s): 1200 g