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Question

A man has three buckets, one can hold exactly 5 litres, tho other exactly 3 litres and the last one exactly 8 litres.
The last bucket is full with 8 litres of petrol in it.
Now another man needs exactly litres of petrol, while he cant make any guesses in getting the petrol and he can use the buckets as many time as he needs to..He needs accurate 4 litres of petrol! ANyONE HAS ANY ANSWERS ON THIS?

Answer 1

Fill up the 5 litre bucket with petrol. Pour some of it into the 3L bucket until it's full. What remains in the 5L bucket will now be exactly 2L. Pour that amount into the 8L bucket.

Pour the petrol in the 3L bucket back into the 5L. Add some more petrol to that bucket until it's back up to a full 5L. Repeat the step in the first paragraph: pour the petrol in the 5L bucket into the 3L until it's full, and pour the 2L that remains in the 5L bucket into the 8L bucket.

Having done this twice, there's now exactly 4L of petrol in the 8L bucket.

There is, of course, 3L of petrol left over in the 3L bucket. You didn't say that leftover petrol was a problem, so I'll assume it's not. :-)

Answer 2

From the 8 liter bucket, fill the 5 liter bucket. then fill the 3 liter bucket rom the 5 liter bucket. Empty the 3 liter bucket back into the 8 liter bucket. Then pour the remaining 2 liters from the 5 liter bucket into the 3 liter bucket. Refill the 5 liter bucket and top off the 3 liter bucket from the 5 liter bucket. The 5 liter bucket will now hold exactly 4 liters.