Answer :
you need to add 3.43 liters of pure alcohol to reach a concentration of 30%.
How much pure alcohol should they add to 12L of the 10% mixture?
Let's define the variable x as the number of liters of the 30% that you need to use.
The concentration of the mixture then will be:
1*x + 0.1*12
Where the concentration for the x liters is 100%, because this is pure alcohol, and for the 12 liters we use a concentration of 10%.
Now, that must be equal to a mixture with a concentration of the 30%, then we can write:
x + 0.1*12 = (x + 12)*0.3
Now we just need to solve this linear equation for x.
x + 1.2 = x*0.3 + 12*0.3
x - x*0.3 = 12*0.3 - 1.2
x*0.7 = 12*0.3 - 1.2
x = (12*0.3 - 1.2)/0.7 = 3.43
This means that you need to add 3.43 liters of pure alcohol to reach a concentration of 30%.
If you want to learn more about linear equations:
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