dans ou en

Radhika, 

Regardless of whether talking about an action starting or finishing, the choice between ' dans ' and ' en ' depends on whether you are 

describing/emphasising the point in time at which 'it' will happen (dans), 

or 

the period of time necessary/during which 'it' will happen (en). 

Just as in English, there is a difference in emphasis between using ' in ' or ' within ', as discussed in the lesson attached. It is not necessarily exclusively one word or the other, but the choice of word changes the meaning. 

 En vs Dans with time (French Prepositions of Time)

Just to provide a few examples to Maarten's explanation:

Il est 11h58, tu dois terminer dans 2 minutes. -- It's 11:58, you have to finish in 2 minutes.

In this example, the emphasis is on fact that something has to be finished by noon. The observation that there are 2 minutes left is secondary.

Tu dois terminer en 2 minutes. -- You have to finish in (within) 2 minutes.

Here, it is secondary what time you have to be finished by. All that counts is that you have 2 minutes to do it.

In everyday usage, the examples will not always be as clear-cut as the ones above. But the emphasis on either the ending (dans) or the period (en) is what determines which one to use.

Thanks Chris and Maarten

With no context, "en" is a possible answer - the only clue is that the question is testing the lesson about the use of "dans".

With no context, "en" is a possible answer - the only clue is that the question is testing the lesson about the use of "dans".

With no context, "en" is a possible answer - the only clue is that the question is testing the lesson about the use of "dans".

Agree Anne

If there was an English translation or original phrase given, the use of ' in ' translates to ' dans ', while the use of ' within ' translates to ' en '.