Two identical pails Q and R contained some water. Pail Q was ¹₈ filled and Pail R was ¹₉ filled. The ratio of the total mass of Pail Q and the water in it to the total mass of Pail R and the water in it was 13 : 12. The total mass of the two pails and the water they contained was 4250 g. What is the mass of an empty pail?
Mass of Pail Q and the water inside = 13 u
Mass of Pail R and the water inside = 12 u

Total mass of the two pails and the water inside them
= 13 u + 12 u
= 25 u

25 u = 4250

1 u = 4250 ÷ 25 = 170

Mass of Pail Q and the water in it more than mass of Pail R and the water in it 
= 13 u - 12 u
= 1 u

Fraction of the water that Pail Q had more than Pail R 
= 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
= 12 u - 8 u
= 4 u
= 4 x 170
= 680 g

Answer(s): 680 g