An oil tanker can be emptied by the main pump in 5 hours. an auxiliary pump can empty the tanker in 12 hours. if the main pump is started at 5 pm, when should the auxiliary pump be started so that the tanker is emptied by 9 pm?

Auxiliary pump should be started at 6:36 PM

Step-by-step explanation:

Let the volume of oil tanker be V.

An oil tanker can be emptied by the main pump in 5 hours,

An auxiliary pump can empty the tanker in 12 hours,

We need to find when should the auxiliary pump be started so that the tanker is emptied by 9 PM if the main pump is started at 5 PM.

Difference in times = 4 hours

That is main pump works for 4 hours and let auxiliary pump works for t hours.

We have

So auxiliary pump works for 2.4 hours,

It should be  started at 9 - 2.4 = 6.6 PM = 6:36 PM

Auxiliary pump should be started at 6:36 PM

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hope this ! have a great day.

-wfz