Two identical tanks J and K contained some water. Tank J was ¹₅ filled and Tank K was ¹₆ filled. The ratio of the total mass of Tank J and the water in it to the total mass of Tank K and the water in it was 11 : 10. The total mass of the two tanks and the water they contained was 3360 g. What is the mass of an empty tank?
Mass of Tank J and the water inside = 11 u
Mass of Tank K and the water inside = 10 u

Total mass of the two tanks and the water inside them
= 11 u + 10 u
= 21 u

21 u = 3360

1 u = 3360 ÷ 21 = 160

Mass of Tank J and the water in it more than mass of Tank K and the water in it 
= 11 u - 10 u
= 1 u

Fraction of the water that Tank J had more than Tank 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 tank
= 10 u - 5 u
= 5 u
= 5 x 160
= 800 g

Answer(s): 800 g