Two identical tanks F and G contained some water. Tank F was ¹₇ filled and Tank G was ¹₈ filled. The ratio of the total mass of Tank F and the water in it to the total mass of Tank G and the water in it was 11 : 10. The total mass of the two tanks and the water they contained was 2520 g. What is the mass of an empty tank?
Mass of Tank F and the water inside = 11 u
Mass of Tank G 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 = 2520

1 u = 2520 ÷ 21 = 120

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

Fraction of the water that Tank F had more than Tank G 
= 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
= 10 u - 7 u
= 3 u
= 3 x 120
= 360 g

Answer(s): 360 g