Two identical tanks W and X contained some water. Tank W was ¹₅ filled and Tank X was ¹₆ filled. The ratio of the total mass of Tank W and the water in it to the total mass of Tank X and the water in it was 10 : 9. The total mass of the two tanks and the water they contained was 2850 g. What is the mass of an empty tank?
Mass of Tank W and the water inside = 10 u
Mass of Tank X and the water inside = 9 u

Total mass of the two tanks and the water inside them
= 10 u + 9 u
= 19 u

19 u = 2850

1 u = 2850 ÷ 19 = 150

Mass of Tank W and the water in it more than mass of Tank X and the water in it 
= 10 u - 9 u
= 1 u

Fraction of the water that Tank W had more than Tank X 
= ¹₅ - ¹₆
= ⁶₃₀ - ⁵₃₀
= ¹₃₀ 

¹₃₀ of the water capacity → 1 u
⁵₃₀ of the water capacity → 5 x 1 u = 5 u

Mass of an empty tank
= 9 u - 5 u
= 4 u
= 4 x 150
= 600 g

Answer(s): 600 g