Answer :
You can fill the 10 gallon pail all the way up. After that, you can pour the water from the 10 gallon pail, into the 4 gallon pail 2 times. That will leave you with 2 gallons in the 10 gallon pail.
You can fill the 10 gallon pail all the way up. After that, you can pour the water from the 10 gallon pail, into the 4 gallon pail 2 times. That will leave you with 2 gallons in the 10 gallon pail.