Honest John says: "What I don't know about milk is scarcely worth mentioning," but he was flabbergasted one day when each of two ladies asked him for two quarts of milk. One lady had a five-quart pail and the other had a four-quart pail. John had only two ten-gallon cans, each full of milk. How did he measure out exactly two quarts of milk for each lady?
It is a juggling trick pure and simple, devoid of trick or device, but it calls for much cleverness to get two quarts of milk into those two pails without making use of any receptacles other than the two pails and the two full cans.
Solution:
Call one ten-gallon (40 quarts) milk can A and the other B, then proceed as follows:
Can A Can B 4 pail 5 pail
1. Initial position: 40 40 0 0
2. Fill 5 pail from can A. 35 40 0 5
3. Fill 4 pail from 5 pail,
leaving 1 quart in 5 pail. 35 40 4 1
4. Empty 4 pail into can A. 39 40 0 1
5. Pour the quart from 5 pail
into 4 pail. 39 40 1 0
6. Fill 5 pail from can A. 34 40 1 5
7. Fill 4 pail from 5 pail,
leaving 2 quarts in 5 pail. 34 40 4 2
8. Empty 4 pail into can A. 38 40 0 2
9. Fill 4 pail from can B. 38 36 4 2
10. Pour from 4 pail into can A
until A is filled, leaving
2 quarts in 4 pail. 40 36 2 2