Question 1149693
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Let me re-write your problem in proper English-Math language.


<pre>
    A tank is 2/3 full. After {{{highlight(cross(drawing))}}} <U>draining</U>  off 120 liters, it's just 1/4 full. 
    What is the {{{highlight(cross(capacities))}}} <U>capacity</U> of the tank. 
</pre>


<U>SOLUTION</U>


<pre>
Let x be the capacity of the tank, in liters.


Then from the condition of the problem


    {{{(2/3)x}}} - 120 = {{{(1/4)x}}}.


It is your basic equation.

To solve it, multiply both sides by 12. You will get


    8x - 120*12 = 3x

    8x - 3x     = 120*12

    5x          = 1440

     x          = {{{1440/5}}} =  288.


<U>ANSWER</U>.  The capacity of the tank is 288 liters.
</pre>

Solved.



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Notice how accurately I use English words, punctuation signs and capital letters, when I start new sentence (!)