How much water should be added to 1 gallon of pure antifreeze to obtain a solution that is 90% antifreeze? I got 1/9, is this correct?

Question

radar · Answer

I think it is correct, I would know for sure if 90% of 1.1111111111 was 1

anonymous · Answer

I think it's 1/10 gallons of water.

If 1 gallon would fit into something to make it filled to 9/10, 
then we would need to fill the rest of the container up with 1/10 of water

radar · Answer

We are asked how much water will be added, not how much pure anti-freeze we are going to throw way!  We are going to end up with more than a gallon, we will still have the 1 gal of pure (expensive) anti-freeze plus whatever water we are to add.  In other words, we are going to dilute this antifreeze so that 1 gal of antifreeze is 90% of the mixture.
Lets call the diluted amount as x.  we know that the antifreeze is going to be .9 or 9/10 of this mixture.  We know that there will be 1 gal of antifreeze so we now can set up the equation.

(9/10)x = 1

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