475. Listening to Someone Else's Bracha

Brachos 1:11

When one person listens to another recite a bracha in its entirety and he has the intention to fulfill his obligation, he has fulfilled it even if he did not answer amen. One who does answer amen is considered as if he recited the bracha himself, so long as the one who recited the bracha was obligated in that bracha. If the one who recites the bracha is only obligated by rabbinic law, while the one answering amen is obligated by Torah law, then the listener cannot fulfill his obligation unless he repeats the bracha after the one saying it or hears the bracha recited by someone else who is obligated by Torah law.

Brachos 1:12

When a group of people gathers to eat bread or drink wine together, if one recites the bracha and the others respond amen, they may all eat and drink. If they did not intend to eat together, each one coming on his own, each should recite his own bracha even if they all eat from the same loaf. This is only the case with bread and wine; other foods do not require the intention to eat together. Therefore, if one person recited a bracha and everyone else replied amen, they may all eat and drink other foods even though they did not originally intend to dine together.