SOLUTION: 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

Algebra ->  Percentage-and-ratio-word-problems -> SOLUTION: 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       Log On


   

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?  
Found 2 solutions by josgarithmetic, ikleyn:
Answer by josgarithmetic(39627) About Me  (Show Source):
You can put this solution on YOUR website!
---Standard two-or-three linear points example---

Description may be points (time, amountFull).

Points described, (5, 0.5) and (30, 0.75). Equation of a line will take these two points. Find from it, x value when y is 1.


slope %280.75-0.5%29%2F%2830-5%29=0.25%2F25=0.01
highlight_green%28y-0.5=%280.01%29%28x-5%29%29, line in point-slope form
%28y-0.5%29%2F0.01=x-5
x-5=%28y-0.5%29%2F0.01
x=%28y-0.5%29%2F0.01%2B5
highlight_green%28y=1%29;
x=%281-0.5%29%2F0.01%2B5
x=0.5%2F0.01%2B5
highlight%28x=55%29

Answer by ikleyn(52864) About Me  (Show Source):
You can put this solution on YOUR website!
.
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. 


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.

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


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


I would say,  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,  you will  100%  fail such blitz-test.