How many gallons of 90% antifreeze must be mixed with 60 gallons of 15% antifreeze to get a mixture that is 80%?

390 gallons of 90 % antifreeze must be mixed with 60 gallons of 15% antifreeze to get a mixture that is 80%

Solution:

Let "x" be the gallons of 90 % antifreeze

60 gallons of 15 % antifreeze

Then, (x + 60) is the gallons present in final mixture that is 80 %

Therefore, x gallons of 90 % antifreeze is mixed with 60 gallons of 15 % antifreeze to get a mixture that is (x + 60) gallons of 80 %

Thus, a equation is framed:

90 % of x + 15 % of 60 = 80 % of (x + 60)

Solve the above equation for "x"

Thus 390 gallons of 90 % antifreeze must be mixed