how many liters of pure alcohol must ne added to 100 liters of 40 percent isopropyl alcohol in order to make 70 percent isopropyl alcohol?
add up the alcohol in the parts and make sure it is the same as the alcohol in the mixture. If x liters of pure 100% alcohol are added, then we must have
.40*100 + 1.00*x = .70(100+x)
Now just solve for x