To fill a tank measuring 40 cm by 50 cm by 20 cm completely, it takes Tap D 10 minutes while it takes Tap E only 12 minutes. How long will it take to completely fill the container with water if both the taps are turned on at the same time and 7 cubic containers of edges 10 cm, filled to the brim with water are poured into the tank?
Volume of the tank 
= 40 x 50 x 20
= 40000 cm³

Volume of 7 containers
= 10 x 10 x 10 x 7
= 7000 mℓ

Remaining volume to be filled by the Tap D and Tap E 
= 40000 - 7000
= 33000 mℓ
= 33000 cm³

Fraction of the tank to be filled
= ³³⁰⁰⁰₄₀₀₀₀
= ³³₄₀

Tap D:
1 tank → 10 min
1 min → ¹₁₀ tank

Tap E:
1 tank → 12 min
1 min → ¹₁₂ tank

Tap D and Tap E:
1 min → ¹₁₀ + ¹₁₂ = ⁶₆₀ + ⁵₆₀ = ¹¹₆₀ tank
1 tank → ⁶⁰₁₁ min

³³₄₀ tank → ⁶⁰₁₁ x ³³₄₀ = ⁹₂ = 4.5 min

Answer(s): 4.5 min