Two identical tanks A and B contained some water. Tank A was ¹₈ filled and Tank B was ¹₉ filled. The ratio of the total mass of Tank A and the water in it to the total mass of Tank B and the water in it was 11 : 10. The total mass of the two tanks and the water they contained was 3570 g. What is the mass of an empty tank?
Mass of Tank A and the water inside = 11 u
Mass of Tank B and the water inside = 10 u

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

21 u = 3570

1 u = 3570 ÷ 21 = 170

Mass of Tank A and the water in it more than mass of Tank B and the water in it 
= 11 u - 10 u
= 1 u

Fraction of the water that Tank A had more than Tank B 
= 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 tank
= 10 u - 8 u
= 2 u
= 2 x 170
= 340 g

Answer(s): 340 g