Two identical tanks C and D contained some water. Tank C was ¹₄ filled and Tank D was ¹₅ filled. The ratio of the total mass of Tank C and the water in it to the total mass of Tank D and the water in it was 9 : 8. The total mass of the two tanks and the water they contained was 2550 g. What is the mass of an empty tank?
Mass of Tank C and the water inside = 9 u
Mass of Tank D and the water inside = 8 u

Total mass of the two tanks and the water inside them
= 9 u + 8 u
= 17 u

17 u = 2550

1 u = 2550 ÷ 17 = 150

Mass of Tank C and the water in it more than mass of Tank D and the water in it 
= 9 u - 8 u
= 1 u

Fraction of the water that Tank C had more than Tank D 
= ¹₄ - ¹₅
= ⁵₂₀ - ⁴₂₀
= ¹₂₀ 

¹₂₀ of the water capacity → 1 u
⁴₂₀ of the water capacity → 4 x 1 u = 4 u

Mass of an empty tank
= 8 u - 4 u
= 4 u
= 4 x 150
= 600 g

Answer(s): 600 g