Question 61079
Suppose that'x' litres of 18% alcohol is taken.
Then quantity of 10% alcohol needed = (20 - x)litres.[as the total is 20 liters]
Thus the equation becomes
x*0.18 + (20-x)*0.10 = 20*0.15
==> 0.18x + 2 - 0.10x = 3
==> 0.08x + 2 = 3
==> 0.08x + 2 - 2 = 3 - 2
==> 0.08x = 1
==> 0.08x/0.08 = 1/0.08
==> x = 1/0.08
==> x = 12.5

So the quantity of 18% alcohol = 12.5 liters
The quantity of 10% alcohol = 20 - 12.5
                            = 7.5 liters

Thus 12.5 liters of 18% alcohol is added to 7.5 liters of 10% alcohol to arrive at 20 liters of 15% alcohol.


Good Luck!!!