In preposition usage

Question

Please help me understanding the usage of in

Four in ten are employed full-time. {Does this mean 4 are working full-time and other 6 part-time}

​​​​ In indicates the style or composition of recorded material. { What's meaning of composition here ? I read the google definition and cannot understand}

The letter was written in ink.
They printed the photographs in duplicate. {They print more than one copy ..right ?}

In indicates composition of money. { What's meaning of composition here ?}

She always pays in cash.
I have six dollars in change.

She hung her head in disappointment. {What's meaning of hung here ?}

In can mean on the occasion of. {Please explain this in detail}

She smiled in acceptance.
He nodded his head in agreement.

Thanx in advance !!!

Answer 1

1. Yes. "in" in that context means "out of": 4 out of 10 people are working full-time; the rest (6 out of 10) are working part-time.
2. The first google definition of "composition" is directly applicable here. It means "made out of". In the case of art, if it is "in ink," that means that the artist used ink to create it. "In duplicate" means that more than one copy was made, as you said.
3. Composition here means exactly the same as above: what the money is "composed of," or what types of money make up the spoken-of sum. Paying "in cash" means that the money transferred is cash (rather than a check or credit card, for example).
4. "Hang one's head" is an idiom that means "look down in shame," or sometimes figuratively means "feel ashamed." See Cambridge Dictionary.
5. "She smiled in acceptance" means that her smile indicated that she accepted something, or that it occurred because she accepted something. The same applies for "nodding in agreement": the nodding indicates agreement, or just is a result of his agreement.