Question 1159216
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Let a = # of singers for school A;  b = #  of singers for school B.


Then from the condition, you have these equations

       a +    b = 40

    0.4a + 0.2b = 0.325*40


or, equivalently

       a +    b = 40     (1)

    0.4a + 0.2b = 13.    (2)


From equation (1), express b = 40-a  and substitute it into equation (2), replacing "b" there


    0.4a + 0.2*(40-a) = 13

    a = {{{(13 -0.2*40)/(0.4-0.2)}}} = 25.


<U>ANSWER</U>.  25 singers are for school A;  the rest,  40-25 = 15 are for school B.
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Solved.