Two identical tanks K and L contained some water. Tank K was ¹₅ filled and Tank L was ¹₆ filled. The ratio of the total mass of Tank K and the water in it to the total mass of Tank L and the water in it was 11 : 10. The total mass of the two tanks and the water they contained was 3780 g. What is the mass of an empty tank?
Mass of Tank K and the water inside = 11 u
Mass of Tank L 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 = 3780

1 u = 3780 ÷ 21 = 180

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

Fraction of the water that Tank K had more than Tank L 
= 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 180
= 900 g

Answer(s): 900 g