To fill a tank measuring 60 cm by 40 cm by 20 cm completely, it takes Tap Q 20 minutes while it takes Tap R only 30 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 9 cubic containers of edges 8 cm, filled to the brim with water are poured into the tank? Leave your answer in minutes and round off to 2 decimal places.
Volume of the tank 
= 60 x 40 x 20
= 48000 cm³
= 48000 mℓ

Volume of 9 containers
= 8 x 8 x 8 x 9
= 4608 cm³ 
= 4608 mℓ

Remaining volume to be filled by the Tap Q and Tap R 
= 48000 - 4608
= 43392 mℓ
= 43392 cm³

Fraction of the tank to be filled
= ⁴³³⁹²₄₈₀₀₀
= ¹¹³₁₂₅

Tap Q:
1 tank → 20 min
1 min → ¹₂₀ tank

Tap R:
1 tank → 30 min
1 min → ¹₃₀ tank

Tap Q and Tap R:
1 min → ¹₂₀ + ¹₃₀ = ³₆₀ + ²₆₀ = ¹₁₂ tank

1 tank = ¹²₁ min

¹¹³₁₂₅ tank = ¹²₁ x ¹¹³₁₂₅ = ¹³⁵⁶₁₂₅ = 10.848

Answer(s): 10.85 min