When Marcos walked into the room, we turned on the lights and yelled, "Happy birthday!"

is this correct punctuation?

Yes! :-)

is this sentence punctuated correctly ?My grandfather's favorite quotation is E.E. Cummings's, "The most wasted of all days is one without laughter."

Yes, the punctuation in the sentence you provided is correct. It consists of a comma and two sets of quotation marks.

When using quotation marks to indicate direct speech or dialogue, you should place the punctuation inside the closing quotation mark. In this case, the exclamation mark goes inside the closing quotation mark after "Happy birthday!".

Here's the breakdown of the punctuation in the sentence:

1. Commas: The comma is used to separate the introductory phrase "When Marcos walked into the room" from the main clause "we turned on the lights and yelled, 'Happy birthday!'"

2. Quotation marks: The first set of quotation marks is used to enclose the words spoken by the group, "Happy birthday!" The second set of quotation marks is used to indicate that these words are being reported or mentioned by the narrator.

I hope this explanation helps clarify the punctuation in the sentence. Let me know if there's anything else I can assist you with!