SOLUTION: Hello, Question: The radiator in a certain make of a car needs to contain 40 liters of 40% antifreeze. The radiator now contains 40 liters of 20% antifreeze. How many liters of

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Question 659535: Hello,
Question: The radiator in a certain make of a car needs to contain 40 liters of 40% antifreeze. The radiator now contains 40 liters of 20% antifreeze. How many liters of this solution must be drained and replaced with 100% antifreeze to get the desired strength?
I have tried creating a table like my teacher suggested and am having a difficult time with that method. I know that my goal is to set up a system of equations but I never know where to place the variables and which number corresponds to that variable.
Thanks,
Katie
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

The actual amount of antifreeze required = 40%2840%2F100%29+=+16 liter
The amount of anti freeze present in 40 liters of 20% = 40%2820%2F100%29+=+8 liters
let the amount to be drained be x liters
so the amount of antifreeze drained will be x%2820%2F100%29+=+0.2+x
amount of antifreeze still present is 8+-+0.2x
since+x liters is drained number liters of 100% antifreeze it has
to be added to present 8+-+0.2x

so, we have 8+-+0.2x+%2B+x+=+16
0.8x+=+16-8
x+=+8%2F0.8
highlight%28x+=+10%29 liters -------answer