Two identical tanks M and N contained some water. Tank M was ¹₃ filled and Tank N was ¹₄ filled. The ratio of the total mass of Tank M and the water in it to the total mass of Tank N and the water in it was 9 : 8. The total mass of the two tanks and the water they contained was 1870 g. What is the mass of an empty tank?
Mass of Tank M and the water inside = 9 u
Mass of Tank N 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 = 1870

1 u = 1870 ÷ 17 = 110

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

Fraction of the water that Tank M had more than Tank N 
= ¹₃ - ¹₄
= ⁴₁₂ - ³₁₂
= ¹₁₂ 

¹₁₂ of the water capacity → 1 u
³₁₂ of the water capacity → 3 x 1 u = 3 u

Mass of an empty tank
= 8 u - 3 u
= 5 u
= 5 x 110
= 550 g

Answer(s): 550 g