Two identical tanks J and K contained some water. Tank J was ¹₇ filled and Tank K was ¹₈ filled. The ratio of the total mass of Tank J and the water in it to the total mass of Tank K and the water in it was 12 : 11. The total mass of the two tanks and the water they contained was 5520 g. What is the mass of an empty tank?
Mass of Tank J and the water inside = 12 u
Mass of Tank K and the water inside = 11 u

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

23 u = 5520

1 u = 5520 ÷ 23 = 240

Mass of Tank J and the water in it more than mass of Tank K and the water in it 
= 12 u - 11 u
= 1 u

Fraction of the water that Tank J had more than Tank K 
= ¹₇ - ¹₈
= ⁸₅₆ - ⁷₅₆
= ¹₅₆ 

¹₅₆ of the water capacity → 1 u
⁷₅₆ of the water capacity → 7 x 1 u = 7 u

Mass of an empty tank
= 11 u - 7 u
= 4 u
= 4 x 240
= 960 g

Answer(s): 960 g