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A hemi-spherical tank of radius \(1.75\) \(m\) is full of water. It is connected with a pipe which empties the tank at the rate of \(7\) litre per second. How much time will it take to empty the tank completely?
 
Answer:
 
Time taken to empty the tank \(=\)  minutes
  
[Note: Round off the minutes to whole number.]