1. When did they arrive at Yosemite?

- They arrived at Yosemite in the afternoon on July 20.

1-2. When did they arrive at Yosemite?
- They arrived at Yosemite in the afternoon on July 20, Friday.

1-3. When did they arrive at Yosemite?
- They arrived at Yosemite in the afternoon, Friday, on July 20.

2. What day did they arrive at Yosemite?
- They arrived at Yosemite on Friday.

3. What date did they arrive at Yosemite?
They arrived at Yosemite on July 20th.

(Are they all grammatical? Would you correct some errors?)

In 1, I'd use "of" instead of "on."

In 1-2, I'd add "a" in front of "Friday."

In 1-3, I'd omit "on."

2 and 3 are fine.

1. When did they arrive at Yosemite? - They arrived at Yosemite in the afternoon on July 20.

- This sentence is grammatically correct and provides a clear answer to the question.

1-2. When did they arrive at Yosemite? - They arrived at Yosemite in the afternoon on July 20, Friday.
- This sentence is also grammatically correct. However, it is more common to place the day of the week before the date, so a more commonly used form would be "They arrived at Yosemite on Friday, July 20th, in the afternoon."

1-3. When did they arrive at Yosemite? - They arrived at Yosemite in the afternoon, Friday, on July 20.
- This sentence is grammatically correct, but it is not the most commonly used form. It is more common to put the day of the week before the date, so a more commonly used form would be "They arrived at Yosemite on Friday, July 20th, in the afternoon."

2. What day did they arrive at Yosemite? - They arrived at Yosemite on Friday.
- This sentence is grammatically correct and provides a clear answer to the question.

3. What date did they arrive at Yosemite? They arrived at Yosemite on July 20th.
- This sentence is grammatically correct and provides a clear answer to the question.