Two identical containers N and P contained some water. Container N was ¹₃ filled and Container P was ¹₄ filled. The ratio of the total mass of Container N and the water in it to the total mass of Container P and the water in it was 6 : 5. The total mass of the two containers and the water they contained was 1870 g. What is the mass of an empty container?
Mass of Container N and the water inside = 6 u
Mass of Container P and the water inside = 5 u

Total mass of the two containers and the water inside them
= 6 u + 5 u
= 11 u

11 u = 1870

1 u = 1870 ÷ 11 = 170

Mass of Container N and the water in it more than mass of Container P and the water in it 
= 6 u - 5 u
= 1 u

Fraction of the water that Container N had more than Container P 
= 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 container
= 5 u - 3 u
= 2 u
= 2 x 170
= 340 g

Answer(s): 340 g