Question

A tap can fill a tank in 6 hours. After half the tank is filled three more similar taps are opened. What is the total time taken to fill the tank completely ?
A) 4 hrs 15 min
B) 3 hrs 24 min
C) 4 hrs 51 min
D) 3 hrs 45 min

Answer 1

Time taken to fill half tank = 3hours.

Now the tap should be kept opened for 3 more hours to full the tank. But now 4 taps are opened insteed of one.

1 tap would take 3 hours. 4taps will take 3/4 hours=45minutes.

So total time

= 3hrs 45minutes

Answer 2

$\underline{\underline{\Huge\mathfrak{Answer ;}}}$

Let total capacity of tank = 6 units

∴∴ Effieciency of A/hr.=66=166=1unit

Half tank capacity=62=362=3units

It will be filled in = 3 hrs 

According to question, 

3 more taps of capacity (1 unit/ hr) are opened with first tap 

Total capacity of 4 taps = 4 units/hrs 

They will fill the tank in ;-

$= > remaining \: capacity \: \div efficiency$

$= > 3units \: \div 4units \: by \: h$

=> 3/4 hours

Total time = 3*3/4 hours = 3 hours 45 minutes.

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@dmohit432