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It's a sunny afternoon, and you want to hang your recently washed clothes(shirts, trousers, shorts etc).
There are 2 identical trees in your yard,both having 10 cm diameters of bodies and they are 4 meters apart from each other, and you want to hang your clothes between them.
You have infinite amount of ropes, each having 2 meters of length.

Trying to use as few ropes as possible, exactly how many ropes do you have to use, without doing any harm to the clothes( don't let them fly away with the wind, don't let them to have stains,dirt,mud etc.)

Edit 1: 3 is the most rational answer. However i should stress this out:
Trying to use as few ropes as possible without doing any harm to the clothes

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closed as too broad by Beastly Gerbil, feelinferrety, boboquack, Mithrandir, Rubio Sep 11 '17 at 14:01

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ is this actually a geometry question more than lateral-thinking? :) $\endgroup$ – Oray Sep 6 '17 at 8:45
  • $\begingroup$ Well, lateral thinking should be the most convenient tag to this question. :) $\endgroup$ – Burak Mete Sep 6 '17 at 8:49
  • $\begingroup$ Are the ropes strechable (to say 50% more of there original length) ? $\endgroup$ – Mea Culpa Nay Sep 6 '17 at 9:59
  • $\begingroup$ No they are not strechable. 2 meters tops. $\endgroup$ – Burak Mete Sep 6 '17 at 10:33
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    $\begingroup$ This is a poorly defined question. The fact that you've written comments on various answers disallowing them for reasons not stated in the question demonstrates this. You haven't even stated how much length of rope you need to affix your clothes to it. $\endgroup$ – AndyT Sep 7 '17 at 10:59
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We need

2 ropes at the least

What I thought,

Tie up both the ropes with individual tree. Now, measure the gap between both and use one trouser's (as they will not harm) belt hooks to tie up the ropes. We can use shirt's sleeves etc as well.
See my version of image posted by @Oray enter image description here

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  • $\begingroup$ Well, this is really close to the solution. But i have not provided/mentioned a stick in the question. There's only the body of the tree, clothes and unlimited ropes. $\endgroup$ – Burak Mete Sep 6 '17 at 11:43
  • $\begingroup$ Why a diagonal stretch/join ? That tends to be longer. Have it either top to top or bottom to bottom (or even Right-most edge of left-hand tree and left-most edge of right-hand tree ...which further optimizes the length)! $\endgroup$ – Mea Culpa Nay Sep 6 '17 at 11:59
  • $\begingroup$ @MeaCulpaNay the joint will be straight. I have just used the Oray's image to explain the logic not the actual measurement. $\endgroup$ – Anurag Sep 6 '17 at 12:04
  • $\begingroup$ @BurakMete I have edited my answer. See the edits and if this is the solution you are looking for. $\endgroup$ – Anurag Sep 6 '17 at 12:05
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    $\begingroup$ -Only uses items provided -Used minimum amount of ropes -Did not make any harm to the clothes as specifically mentioned in the question $\endgroup$ – Burak Mete Sep 6 '17 at 13:00
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Lateral thinking, so:

0? You could presumably tie each item of clothing to the next, connecting sleeves to legs, etc., making a rope of sorts from the items you wish to dry. This assumes that the trees are very clean.

Alternatively:

2, one around each tree with a couple of socks tied-in to close the gap between them

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  • $\begingroup$ Good approach, but its not that realistic. Although the primary goal is to use as few ropes as possible, tying clothes on trees could harm them. But this was a good way of thinking. $\endgroup$ – Burak Mete Sep 6 '17 at 9:10
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Depending on exactly what the trees are like,

it should be pretty easy to get away with just two ropes by taking advantage of either (1) the fact that trees have branches, and surely they will have branch-parts that are closer together than the 4m separation between the trunks, or (2) the fact that tree trunks are a little bit flexible, so even if for some reason you can only attach the ropes to the trunks you can probably get just-under-4m of rope to connect them by making them bend towards one another.

If you're lucky

you may well be able to manage just one rope by the same means; again, it depends on how long the branches are and where they are.

I remark that

both of these approaches involve lateral thinking in a rather literal sense: lateral branches and/or lateral bending of the trunks. :-)

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  • $\begingroup$ I should have mentioned that "closest difference between the trees are 4 meters", so the closest you can get is with the body of the tree. But +1 for the way of thinking. $\endgroup$ – Burak Mete Sep 6 '17 at 10:39
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I'd say that you would need

0 ropes

How?

Just put a clothes horse in between the two trees and hang your clothes there.


If the above answer doesn't satisfy you, you can also do it with

1 rope

But you will need some extra's:

Cut off a piece of wood from these trees that is 4 meters long, then cut your rope in 2 and attach the ends of the stick to the trees. Hang your clothes on that stick


EDIT

Apparently you can only use the items mentioned in the question.

In this case you will most probably be able to achieve this using only

2 ropes.

Here's how:

We know that the trees are 10cm in diameter, so we will need $2*Pi*R$ cm of rope to go around one of the trees. So for each tree we need approximately $31.42$ cm of rope. For both trees it would become $62.84$ cm. And now the interesting part:
It is not given how many clothes do we have, nor what type of trees are they. Assuming they are not old, dead, dry trees that will break if you push on it, we can do the following:

Attach one rope to each tree at the same height(the higher - the better). Then, start pulling the other ends of the ropes until you can knot a knot. Given that the trees are only 10cm in diameter, it should not be that difficult to pull them closer to each other.

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  • $\begingroup$ You have only the items that mentioned in the question. In this case, body of the tree, clothes, and unlimited amount of ropes. $\endgroup$ – Burak Mete Sep 6 '17 at 11:44
  • $\begingroup$ I agree with the idea of your final solution, but you only need one rope (assuming that you can manually bend the trees together and then tie them. $\endgroup$ – AndyT Sep 7 '17 at 10:57
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This is a solution using an optimization and geometry way of thinking instead of lateral-thinking. Because I like it in this way :)

enter image description here

I did not add the calculation part since OP said this is actually lateral-thinking question. But

3 ropes will be enough anyway.

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  • $\begingroup$ Yeah, this looks like the most obvious way to do it.However it's like the worst case scenario. Do you think it's possible to do it with less then 3 ropes? $\endgroup$ – Burak Mete Sep 6 '17 at 9:09
  • $\begingroup$ @BurakMete this is not lateral-thinking solution :) $\endgroup$ – Oray Sep 6 '17 at 9:10
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We need

3 ropes

As

2 ropes to cover the 4m distance between the trees and another 1.2m is needed to tie the ropes around the trees (2*pi*0.1 m + 2 * pi * 0.1 m = 1.2m approx) and hence we need one more !

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  • $\begingroup$ Yes, this is an obvious solution but there's a solution where you can use less. $\endgroup$ – Burak Mete Sep 6 '17 at 10:34
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    $\begingroup$ your calculation is wrong, only 0.6m is needed, not 1.2m $\endgroup$ – Novarg Sep 6 '17 at 11:10
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Depending on the nature of the ropes, perhaps you can

divide a single rope into multiple strands that you can tie together to make a longer but thinner (and weaker) rope. Clothes are not very heavy and this will surely still be strong enough.

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I would try

0 ropes

Can't we just

hang the washing on the branches?

If that doesn't satisfy, then you could try

1 rope

By

Tying the rope between branches of the same tree, rather than between them. This assumes that 2m is long enough to hang all the washing on, but then most of the other answers have similar assumptions.

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