Thanks!!...Clock, what clock? ;)

----------

Fill up the 5-gallon cone with water. Then dump water into the 3-gallon cone until full. This will leave 2 gallons in the 5-gallon cone. Mark the cone indicating where the 2 gallon mark is.

Two of those will yield exactly 4 gallons.

close, but get 4 gallons into the 5 gallon holder.
forget the picture. just simply two upside down cone canisters.

Can you use a ruler to measure the height of each of the cones?

If so, a cone is always half full when the water depth is 79.37% of the cone height (cubed root of 1/2), which applies regardless of cone taper.

Both cones can then be filled half full, which gives 2.5 gal and 1.5 gal. The combination is then 4 gal.

Can I use a scale?
Piece o' cake, then...;)

That would work too!

Do you need a thermometer though so that you know the density of the water?

nope.....and........nope

Okay...
Fill the 5-gallon cone, then dunk the 3-gallon cone inside it until the 3 gallons spills out. Now there's 2 gallons inside the 5-gallon cone.

Float the 3-gallon cone inside it and fill it until the water levels are equal.

Dump the 2 gallons now inside the 3-gallon cone inside the 5-gallon cone.

Fill 5 gallon dump into 3 gallon, empty 3 gallon. Pour 2 gallons from 5 gallon container into 3 galllon container. Fill 5 gallon container and empty 1 gallon into three gallon leaving 4 gallons in 5 gallon container. Problem is this breaks rule 1 but is the only way I know to do it.

How thick are these cones?

Go with Daze's first part by taking the full 5 gal cone, pouring it into the 3 gal, emptying the 3 gal, and pouring the remaining 2 gal into the 3 gal cone. Then fill the 5 gal, push the 3 gal cone into the 5 gal until the two tops line up, which would leave 2 gal in the 5 gal cone. Pour the 2 gal from the 3 gal cone into the 5 gal cone for a total of 4 gal.

hint: what do you get when you mix a donzi with a baja?
THE ANSWER
!
you guys are real close but abide by the rules.

well folks, it's been fun chatting in the daylight hours, but my time has come to an end. as of may 1 (tomorrow) our company is installing a new broad band useage reduction program.....i.e. making all internet users validate who they are as they go to the outside internet..... not worth the risk of a great career. like they couldn't find out now...... complacency i guess......

"I'm going clean as of NOW. "

see ya on the dark side ( after 9:00pm when the kids are finally in bed and wife is watching her taped soap opera)
it's been fun. too fun and addicting, maybe I'll get some work done now.
at least i don't have 6000+ post like waterfoul in his one year stint behind the PC during the day;)

see ya tonight