SOLUTION: Erasers cost 45 cents apiece. Notebooks cost 90 cents apiece. Karla spent $18 for a total of 28 erasers and notebooks. How many notebooks did she buy

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Question 994078: Erasers cost 45 cents apiece. Notebooks cost 90 cents apiece. Karla spent $18 for a total of 28 erasers and notebooks. How many notebooks did she buy
Found 3 solutions by solver91311, derosejulia, ikleyn:
Answer by solver91311(24713)   (Show Source): You can put this solution on YOUR website!


Let represent the number of notebooks and represent the number of erasers. Then



and



Solve the 2X2 system.

John

My calculator said it, I believe it, that settles it

Answer by derosejulia(1)   (Show Source): You can put this solution on YOUR website!
.90x+.45y=18.00
.90x+.45(28)=18.00
.90x+12.6=18.00
.90x=5.4
x= 6 notebooks
Answer by ikleyn(52787)   (Show Source): You can put this solution on YOUR website!
.

            The solution by @jerosejulia is INCORRECT.

            It becomes obvious if you make a formal check.

            Below find the correct solution. 


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 =  = 12.


Answer.  12 notebooks and 28-12 = 16 erasers.


Check.   12*0.90 + 16*0.45 = 18.00 dollars.   ! Correct !


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