Discussion

Explanation:

The time taken by pump A alone to fill the tank completely = t hours.

The time taken by pump B alone to fill the tank completely = ‘t - 2’ hours.

On Wednesday, pump A was used for 3 hour less and pump B was used for 2 hours to complete the remaining work.
⇒ Work done by A in 3 hours = Work done by B in 2 hours.
⇒ efficiency of A : efficiency of B = 2 : 3

Let efficiency of A be '2x' and that of B be '3x'.

Now, total work is done by B in (t - 2) hours and by A in t hours.
⇒ 3x × (t - 2) = 2x × t
⇒ 3(t - 2) = 2t
⇒ t = 6 hours

∴ The tank starts filling at 2 pm.

If both pumps start filling, their combined efficiency = 5x
Total work to be done = 3x(t - 2) = 12x

⇒ Time taken to fill the tank = 12x/5x = 2.4 hours = 2 hours 24 minutes.

Therefore on Thursday, the tank will be completely full at 4.24 pm.

Hence, option (d).

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