Two identical containers J and K contained some water. Container J was ¹₅ filled and Container K was ¹₆ filled. The ratio of the total mass of Container J and the water in it to the total mass of Container K and the water in it was 8 : 7. The total mass of the two containers and the water they contained was 2400 g. What is the mass of an empty container?
Mass of Container J and the water inside = 8 u
Mass of Container K and the water inside = 7 u

Total mass of the two containers and the water inside them
= 8 u + 7 u
= 15 u

15 u = 2400

1 u = 2400 ÷ 15 = 160

Mass of Container J and the water in it more than mass of Container K and the water in it 
= 8 u - 7 u
= 1 u

Fraction of the water that Container J had more than Container K 
= 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 container
= 7 u - 5 u
= 2 u
= 2 x 160
= 320 g

Answer(s): 320 g