The figure is not drawn to scale. Tank R measuring 50 cm by 47 cm by 20 cm contained 30.35 ℓ of water. Tank S measuring 42 cm by 25 cm by 37 cm contained 21 ℓ of water. Ben poured some water from Tank R into Tank S without spilling and the water level of Tank S rose to 31 cm. What was the height of water level left in Tank R?
1 ℓ = 1000 cm³
21 ℓ = 21000 cm³
30.35 ℓ = 30.35 x 1000 = 30350 cm³

Height of water in Tank S at first
= 21000 ÷ 42 ÷ 25
= 20 cm

Increase in the height of water in Tank S
= 31 - 20
= 11 cm

Volume of water poured into Tank S
= 42 x 25 x 11
= 11550 cm³ 

Volume of water left in Tank R
= 30350 - 11550
= 18800 cm³ 

Height of water left in Tank R
= 18800 ÷ 50 ÷ 47
= 8 cm

Answer(s): 8 cm