Two identical tanks E and F contained some water. Tank E was ¹₅ filled and Tank F was ¹₆ filled. The ratio of the total mass of Tank E and the water in it to the total mass of Tank F and the water in it was 8 : 7. The total mass of the two tanks and the water they contained was 2250 g. What is the mass of an empty tank?
Mass of Tank E and the water inside = 8 u
Mass of Tank F and the water inside = 7 u

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

15 u = 2250

1 u = 2250 ÷ 15 = 150

Mass of Tank E and the water in it more than mass of Tank F and the water in it 
= 8 u - 7 u
= 1 u

Fraction of the water that Tank E had more than Tank F 
= 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
= 7 u - 5 u
= 2 u
= 2 x 150
= 300 g

Answer(s): 300 g