Question 1195293
.
A fish tank in a pet store was less than half full of water 
when a worker turned on a hose to fill the tank at a constant rate. 
After the hose was on for 5 minutes, the tank was exactly half full. 
After the hose was on for 30 minutes, the tank was three-quarters full. 
How many minutes did it take after the hose was turned on for the tank 
to be completely filled with water?  
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            It is a joke Math problem,  and it can be solved in couple of lines
            using simple and elementary reasoning INSTEAD of using complicated formulas.



<pre>
In 30-5 = 25 minutes, the hose fills the tank from 1/2 to 3/4.

In other words, it takes 25 minutes to fill 1/4 of the tank.

It means that in 5 + 25 + 25 = 55 minutes from the start, the tank will be filled in full.
</pre>

Solved, &nbsp;completed and explained.



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The meaning of this problem is to give to a person an opportunity to find simple/simplest solution.



In such form, &nbsp;it is accessible to any &nbsp;3th grade young student,
and it &nbsp;REALLY &nbsp;teaches him &nbsp;(or her) &nbsp;to think in a right way and do not make unnecessary job.



It is also good for those older than &nbsp;70 &nbsp;as an entertainment problem.



I would say, &nbsp;it also good as a blitz-test problem at the job-hiring interview 
to determine if a person is able to think creatively.



Let god save you from solving it in this way as @josgarithmetic proposes to do it in his post.



Doing that way in the interview, &nbsp;you will &nbsp;100% &nbsp;fail such blitz-test.