SOLUTION: An automobile radiator contains 16 liters of antifreeze and water. This mixture is 30% antifreeze. How much of this mixture should be drained and replaced with pure antifreeze so t

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Question 225271: An automobile radiator contains 16 liters of antifreeze and water. This mixture is 30% antifreeze. How much of this mixture should be drained and replaced with pure antifreeze so that there will be 50% antifreeze?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let x = liters of mixture to be drained
and replaced with pure antifreeze.
In words:
(liters of antifreeze I end up with)/(final total liters in radiator) = 50%
Notice that I start with 16 liters in the radiator
and I end up with 16 liters in the radiator, so I can write
(liters of antifreeze I end up with)/16 = 50%
16 liters of 30% antifreeze has .3%2A16+=+4.8 liters antifreeze
I drain out x liters, and in doing so, I remove .3x liters
antifreeze
So far, I've got 4.8+-+.3x liters antifreeze in radiator
Now I pour in x liters of antifreeze
I end up with 4.8+-+.3x+%2B+x liters antifreeze
My equation is then
%284.8+%2B+.7x%29%2F16+=+.5
4.8+%2B+.7x+=+8
.7x+=+3.2
x+=+4.571 liters
4.571 liters need to be drained out and
replaced with pure antifreeze
check answer
If I replace x with a 30% mixture again, I'll be back
to 30% in the whole radiator
.3%2A4.571+=+1.371 liters antifreeze
16+-+4.571+=+11.429
.3%2A11.429+=+3.429 liters antifreeze in rest of radiator
%281.371+%2B+3.429%29%2F16+=+.3
4.8%2F16+=+.3
4.8+=+4.8
OK