Tank Problem – Which tank will be filled first?

The Question is – 


  • Air pressure is same on Liquid.
  • flow rate of water pouring in tank 1 through tap is equal to the water going out through the opening.

Trick –  To Solve this problem simply remember that Liquid ( Water ) will be at same level irrespective of size and shape of container. Something like below.


Click For Answer

  1. First water in Tank 1 will get filled upto the connectivity of Tank 1 and Tank2. Then Water will start flowing in Tank 2.


2.  Now water in Tank 2 will get filled UpTo connectivity of Tank 2 and Tank 3. Now Water will start flowing in tank 3.


3. Now coming to tank 3,

  • Here important thing to notice – Outlet of 3 and inlet of 4 are not at same level.
  • Water will rise in tank 3 upto connectivity of tank 3 and tank 4.


  • Now, outlet of Tank 3 is vertical and rises to top at tank 4. So due to this water will rise equally in height in tank 3 and pipe until the height ‘h’ is achieved. Where h is the height of water inlet of tank 4.After this height h is achieved, water will pour to tank 4.


  • We discussed that – Water is always at same level. so tank 4 starts filling and reaches same point in tank 3


  • Now both the tank 3 and 4 will fill simultaneously till they get fully filled.


Hence the answer is 3 and 4 both 🙂

  • For Video Solution check our Video – 

10 Replies to “Tank Problem – Which tank will be filled first?”

    • Logical Baniya

      Then Tank 2 will be filled first. Tank 1 will never get filled as tanks are open.
      Water will start coming out from Tank 2 once Tank 2 and Tank1 reached the same level.
      Hope this helps 🙂

    • moussa

      i agree with you but i think 4 will fill Fraction of a second sooner, because the Pressure at the bottom of 3 is much than above of the 4 then maybe 4 fill sooner at least one molecule!! sooner i will try to experience too!!!

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