Four two-way pipes A, B, C and D can either fill an empty tank or drain the full tank in 4, 10, 12 and 20 minutes respectively. All four pipes were opened simultaneously when the tank is empty. Under which of the following conditions the tank would be half filled after 30 minutes?
Explanation:
Let the capacity of the tank = LCM(4, 10, 12, 20) = 60 units ∴ Efficiency of A, B, C and D = 15, 6, 5, 3 units/minute respectively.
We need to check options now, Option 1: Work Done in a minute = 15 – 6 – 5 – 3 = 1 unit ∴ After 30 minutes, the tank will be half filled.
We don’t have to check other options. Hence, option (a).
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