Question

How can we divide 8litres of water equally in a 5litre and a 3 litre tanks(you can't destroy or construct the tank).
and plzzzz no ridiculous answers this answer costs 20 points

Answer 1

The answers you get are ridiculous because the question sounds ridiculous.
(it would help if you typed the original question word for word or added a picture of it)
Let us consider some cases:

case 1. (assuming you can use more than one of each tanks and the question demands separate answers for 5 and 3 liters.)

Ans: a. two 5L tanks with 4L water in each
b. three 3L tanks with 8/3=2.667L of water

case 2: (Assuming both tanks are to be used in conjunction)

ans: a 5 litre tank and two 3L tanks with 8/3 L each

case 3: (assuming the cans are to be used just as measuring devices to split the 8L water into equal parts [4L each] )

ans: Take a destination tank of 4L. Fill the five litre tank to the brim and then pour water from it into the three liter can. This will give you 2L water left in the 5L can. Move this to another can where 4L is required ( destination tank). Refill the 5L can with the water from the 3L tank and the remaining water from source tank. Repeat the above step to get another 2L water in the 5L tank. Now pour this into the destination tank. now we have 4L in the destination tank and 4L with us and thus we've divided the water into equal parts.

Answer 2

fill 3 litre tank than put these 3 litre in 5litre tank than again fill 3lt and than put it in the space remaining in 5lt tank 1 lt remains in the 3lt tank . than drop the 5lt from the 5lt tank put the 1lt in the 5lt tank and than fill the 3 lt tank 3+1 = 4