question no 1

5L contents 3L contents Fill 5L with water 5L 0L Fill 3L from 5L 2L 3L Empty 3 L 2L 0L Put the remainder from the 5L into the 3L, 0L 2L Fill the 5L 5L 2L Top the 3L up from the 5L leaving 4L in the 5L. 4L 3L QED.

this problem is similar to that of the movie "Die Hard" with Bruce Willis and Samuel L Jackson. first, fill up with water the 3L bucket. transfer it to 5L bucket. fill the 3L bucket with the remaining 2L of water. mark the 3L bucket where 2L of water measures. fill up the 3L bucket with water from the 5L bucket. drain the water from the 3L bucket down to the mark. fill with the remaining 2L of water in 3L bucket into the 5L bucket which has 2L of water remaining. and the problem is solved, you get exactly 4L of water in 5L bucket.

i knew the answer but forgot.mmm... anyway i will check another time i am sure i can answer this one!