Two identical tanks G and H contained some water. Tank G was ¹₇ filled and Tank H was ¹₈ filled. The ratio of the total mass of Tank G and the water in it to the total mass of Tank H and the water in it was 11 : 10. The total mass of the two tanks and the water they contained was 5040 g. What is the mass of an empty tank?
Mass of Tank G and the water inside = 11 u
Mass of Tank H 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 = 5040

1 u = 5040 ÷ 21 = 240

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

Fraction of the water that Tank G had more than Tank H 
= 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 240
= 720 g

Answer(s): 720 g