Two identical pails J and K contained some water. Pail J was ¹₈ filled and Pail K was ¹₉ filled. The ratio of the total mass of Pail J and the water in it to the total mass of Pail K and the water in it was 11 : 10. The total mass of the two pails and the water they contained was 5040 g. What is the mass of an empty pail?
Mass of Pail J and the water inside = 11 u
Mass of Pail K and the water inside = 10 u

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

21 u = 5040

1 u = 5040 ÷ 21 = 240

Mass of Pail J and the water in it more than mass of Pail K and the water in it 
= 11 u - 10 u
= 1 u

Fraction of the water that Pail J had more than Pail K 
= 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 pail
= 10 u - 8 u
= 2 u
= 2 x 240
= 480 g

Answer(s): 480 g