Two identical tanks N and P contained some water. Tank N was ¹₉ filled and Tank P was ¹₁₀ filled. The ratio of the total mass of Tank N and the water in it to the total mass of Tank P and the water in it was 12 : 11. The total mass of the two tanks and the water they contained was 2990 g. What is the mass of an empty tank?
Mass of Tank N and the water inside = 12 u
Mass of Tank P and the water inside = 11 u

Total mass of the two tanks and the water inside them
= 12 u + 11 u
= 23 u

23 u = 2990

1 u = 2990 ÷ 23 = 130

Mass of Tank N and the water in it more than mass of Tank P and the water in it 
= 12 u - 11 u
= 1 u

Fraction of the water that Tank N had more than Tank P 
= ¹₉ - ¹₁₀
= ¹⁰₉₀ - ⁹₉₀
= ¹₉₀ 

¹₉₀ of the water capacity → 1 u
⁹₉₀ of the water capacity → 9 x 1 u = 9 u

Mass of an empty tank
= 11 u - 9 u
= 2 u
= 2 x 130
= 260 g

Answer(s): 260 g