Sunday, 20 March 2011

Pouring water

Answer to previous riddle: There is just as much milk in the tea as there is tea in the milk. As long as the volume of liquid in both cups remain the same at the end (i.e. half the cup), then whatever milk isn't in the milk cup must be in the tea cup. Likewise with the tea.

Very counter-intuitive. Which is why I love this one. The next one comes from a series of similar riddles that involve pouring exact amounts of liquid given odd-sized jug. I was first introduced to these in grade 3!

Given 9L and 5L jugs, give me exactly 6L of water. Their volumes are measured at the brim. The jugs are oddly shaped, but so you cannot estimate any proportion of the jug (i.e. you can't "eyeball" where half is). You cannot put any marks on the jug or otherwise keep track of where water levels were.


  1. Fill up the 5L jug and pour it into the 9L jug, pour into the 5L jug again, pour as much possible into the 9L jug. You'll have 1L left on the 5L jug, empty the 9L jug, pour the 5L jug into the 9L and then another full 5L. Leaving you with 6L in the 9L jug.

    Or is it shorter?

  2. empty the 9L till you feel its about 1L and then pour the 5L into the 1L ?

  3. Umm. I'm taking a shot at this one. Fill the 9L twice using the 5L jug to over fill it and collect the 1L that over flows. Then just fill the 5L jug again. So all together you would have the 5L and the 1L overflow.

    Hmm? Yes?

  4. Got yesterdays riddle correct!

    As for todays, I'm sort of stumped.

  5. 1)Fill 9ltr jug
    9ltr = 9 5ltr = 0
    2) Fill 5ltr from 9ltr jug
    9ltr = 4 5ltr = 5
    3)Empty 5ltr, pour rest of 9ltr into 5ltr
    9ltr = 0 5ltr = 4
    4) Fill 9ltr and use it to fill 5ltr
    9ltr = 8 5ltr = 5
    5) Empty 5ltr, refil from 9ltr
    9ltr = 3 5ltr = 5
    6) Repeat steps 3-5
    9ltr = 0 5ltr = 3
    9ltr = 7 5ltr = 5
    9ltr = 2 5ltr = 5
    7) Repeat steps 3 and 4
    9ltr = 0 5ltr = 2
    9ltr = 6

    Dont think there's a quicker way than that.

  6. Too difficult for me! Can't wait to see the answer.

  7. dang, this is a hard one. I give up.

  8. Using a liquid that is heavier than water, fill the 9L jug, fill the 5L jug from that. Then, empty the 5L jug, and refill it with the remaining 4L in the 9L jug. Fill the rest of the 5L jug with water, and poor that 1L of water into the 9L jug. Then, poor out the heavy liquid, fill the 5L jug with water, poor that into the 9L jug, and you have 6L of water.

  9. i think remember this one. isn't there supposed to be an empty jug that you can use?

  10. I should know this but my brain hurts...
    Fill the 5l jug and pour it into the 9l jug
    Fill the 5l jug again and pour 4l into the 9l jug leaving 1l in the 5l jug
    Empty the 9l jug...
    Tip this 1l (left in the 5l jug) into the 9l jug

    Then fill up the 5l jug and pour it all into the 9l jug totalling 6l

  11. Ah I completely did not think of that. XP

  12. i dont understand- but im thirsty

  13. fill the 5l jug and pour it in the 9l, repeat.
    now you have 1l inside the 5l jug.
    dispose the contents of the 9 l jug and pour the content of the 5l inside the 9l, after taht, fill the 5l and pour inside the 9 l.

    there, do I cookies now?

  14. I know ive done a few of these before, im trying to work it out in my head.

  15. There's obviously a way, but probably is way too complicated.

  16. Pendragon had my idea.


  17. uhmm.. Hmm.. I think I'll just wait for the answer :)