To fill a tank measuring 40 cm by 30 cm by 20 cm completely, it takes Tap C 6 minutes while it takes Tap D only 18 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 5 cubic containers of edges 8 cm, filled to the brim with water are poured into the tank?
Volume of the tank 
= 40 x 30 x 20
= 24000 cm³

Volume of 5 containers
= 8 x 8 x 8 x 5
= 2560 mℓ

Remaining volume to be filled by the Tap C and Tap D 
= 24000 - 2560
= 21440 mℓ
= 21440 cm³

Fraction of the tank to be filled
= ²¹⁴⁴⁰₂₄₀₀₀
= ⁶⁷₇₅

Tap C:
1 tank → 6 min
1 min → ¹₆ tank

Tap D:
1 tank → 18 min
1 min → ¹₁₈ tank

Tap C and Tap D:
1 min → ¹₆ + ¹₁₈ = ³₁₈ + ¹₁₈ = ²₉ tank
1 tank → ⁹₂ min

⁶⁷₇₅ tank → ⁹₂ x ⁶⁷₇₅ = ²⁰¹₅₀ = 4.02 min

Answer(s): 4.02 min