How many times do we need to throw the dice to be sure of 1/2 chance that at least...

[Mehrudin]

How many times do we need to throw 2 dices to be sure that there is a 1/2 chance (probability) that at least once the sum of the dices will be 12?

 

[stapel]

How many times do we need to throw 2 dices to be sure that there is a 1/2 chance (probability) that at least once the sum of the dices will be 12?

What are your thoughts? What have you tried? Where are you stuck?

Please be complete. Thank you!