Question 1176305
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            In both posts by  @ewatrrr and  @MathLover1,  everything including the problem setup,  the solution and the answer, 

            is  WRONG,  INCORRECT  and  IRRELEVANT,


            because these ladies misread the problem and did not take a labor to read the problem attentively and to understand its meaning.


            I came to bring the correct solution.



<pre>
Let x be the number of girls.


Then the total students is  (1200 + x).

The total of those who pays their school fees is  (0.5*1200 + 0.4x) = (600 + 0.4x).


The equation is


    {{{(600+0.4x)/(1200+x)}}} = 0.46.


To solve it, multiply both sides by the denominator and simplify


    600 + 0.4x = 0.46*(1200 + x)

    x = {{{(600-0.46*1200)/(0.46-0.4)}}} = 800.


<U>ANSWER</U>.  The number of girls in the school is 800.
</pre>

Solved.