A chemical plant has four tanks (A, B, C, and D), each containing 1000 litres of a chemical. The chemical is being pumped from one tank to another as follows:
From A to B @ 20 litres/minute
From C to A @ 90 litres/minute
From A to D @ 10 litres/minute
From C to D @ 50 litres/minute
From B to C @ 100 litres/minute
From D to B @ 110 litres/minute
Which tank gets emptied first and how long does it take (in minutes) to get empty after pumping starts?
Explanation:
The change in the amount of chemical in each tank after every minute is as follows:
A: −20 – 10 + 90 = 60
B: −100 + 110 + 20 = 30
C: −50 − 90 + 100 = −40
D: −110 + 10 + 50 = −50 Since tank D loses the maximum amount of chemical in a minute, it will be emptied first.
Let n minutes be the time taken by tank D to get empty.
∴ 1000 – 50n = 0
∴ n = 20 minutes
Hence, option (c).
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