Step 0.
Jug1: volume V of alcohol, concentration 1
Jug2: volume V of water, concentration 1
Step 1. Pour Q of Jug2 into Jug1.
Jug1: volume V of alcohol, concentration V/(V+Q)
volume Q of water, concentration Q/(V+Q)
Jug2: volume V - Q of water, concentration 1
Step 2. Pour Q of Jug1 into Jug2.
Jug1: volume of alcohol = V * V/(V+Q), concentration V/(V+Q)
volume of water = V * Q/(V+Q) , concentration Q/(V+Q)
Jug2: volume of alcohol = Q * V/(V+Q), concentration Q/(V+Q)
volume of water = (V-Q) + Q * Q/(V+Q) = V * V/(V+Q), concentration V/(V+Q)
