Question 994078
.


            The solution by @jerosejulia is INCORRECT.


            It becomes obvious if you make a formal check.


            Below find the correct solution.



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0.90*N + 0.45*(28-N) = 18.00


0.90N + 0.45*28 - 0.45N = 18.00


(0.90-0.45)N = 18.00 - 0.45*28


N = {{{(18.00 - 0.45*28)/(0.90-0.45)}}} = 12.


<U>Answer</U>.  12 notebooks and 28-12 = 16 erasers.


<U>Check</U>.   12*0.90 + 16*0.45 = 18.00 dollars.   ! Correct !
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