Question: When a few people or groups of people give each other something they do not have at first to utilize, which word would be correct to use?

For example, my friends and I have a dictionary while we need more sheets of papers or books. We give them our dictionary and we get allowed to use their books we need. Since we do not take the books or give the dictionary permanently, I doubt that the word exchange is correct. On the other hand, the word share connotes a situation that both groups use the same thing at the same time. Is there a word for the scenario?

Answer: 
Your statement *A is 2 hours within of B* is ungrammatical. It should be 

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> A is within 2 hours of B.
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It means that it would require two hours or less to travel from A to B.
As already pointed out, the phrase is:

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> (something) is (amount) within [of (something else)].
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* My office is **within** 2 miles **of** the bus station.
* The second train departs **within** 5 minutes **of** the first train's arrival.

It is common to drop the last part. In that case, you would normally understand it to mean "now" for time, "here" for space, and so on:

* My office is **within** 2 miles.

== My office is **within** 2 miles **of** here.

* The train departs **within** 5 minutes.

== The train departs **within** 5 minutes **of** now.

For points within a perimeter, **of** is not used:

* These trees are **within** my property.
* The jar is **within** my reach.

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> "A-B=2 hours or B-A=2 hours" 
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Mathematically, you could think of **within** as expressing < (less than) or ≤ (less than or equal to), depending on the situation. Or informally ± (plus or minus).

* The point x is **within** the circle C.

In this situation I would assume you mean strictly less than. I.e. if the point lies exactly on the border of the circle, it is no longer considered to be 'within' the circle:

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> Let d\_x be the distance from the center of circle C to point x.
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> Let r be the radius of C.
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> d\_x < r
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* My house is **within** 2 miles of the train station.

In this situation I would assume mean less than or equal to (≤) rather than strictly less than (<). In other words, if your house is actually exactly 2.000 miles from the train station, you have still made an accurate statement.

* The estimate is **within** 5%.

== The estimated value is within 5% of the true value.

In this situation, I would suspect you mean that the estimate could be less than 5% of the true value, *or* it could be exactly 5% of the true value. I.e. ≤ (less than or equal).

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> Let e be the estimated value.
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> Let v be the true value.
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> v - 0.05v ≤ e ≤ v + 0.05v
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