SOLUTION: To strengthen a mixture of 10% alcohol to 30% alcohol, how much pur alcohol must be added to 7 L of the 10% solution? Can you how me step by step

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Question 177629: To strengthen a mixture of 10% alcohol to 30% alcohol, how much pur alcohol must be added to 7 L of the 10% solution? Can you how me step by step
Answer by Mathtut(3670) About Me  (Show Source):
You can put this solution on YOUR website!
let x be the amount of pure alcohol added
:
existing solution+added solution=final mixture
:
.10(7)=existing
:
x = pure alcohol added
:
.3(7+x)=final mixture(see we want to end up with 30% of what we are mixing and thats the original 7 liters plus what ever we add.
:
so putting it altogether we have
:
.10(7)+x=.3(7+x).....eq 1
:
.7+x=2.1+.3x
:
.7x=1.4
:
highlight%28x=2%29Liters of pure alcohol