a solution of 61% vinegar is to be mixed with a solution of 21% vinegar to form 160 liters of a 44% solution. How many liters of the 61% solution must be used?

Solution:

x liters of the 61% solution must be used

So

61%x+21%(160-x) = 44%*160

x = 92

So 92 liters of the 61% solution must be used