Quandaries and Queries


My question is how do you prepare a 100ml of a 30% alcohol solution using 95% alcohol?
Justin (Student)
Grade 10


Hi Justin,

You want to end up with 100ml of liquid, 30% of which is alcohol. 30% of 100ml is  30/100100 = 30 ml. Thus you need 30 ml of alcohol and 70 ml of water.

The question now is, how much of the 95% solution do you need to give you 30 ml of alcohol? To ask this question using algebra, let x ml be the amount of the 95% solution that you need, then the question becomes

What is x if 95% of x is 30 ml?

Said as an equation, solve for x if

 95/100  x = 30

Can you complete the problem now?



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