354. In and Into
(a) In
(X) Gemma spent all the day into her room.
(O) Gemma spent all the day in her room.
(b) Into
(X) Richard came in the room and sat down.
(O) Richard came into the room and sat down.
"In" denotes position inside something,
while "into" denotes motion or direction towards the inside of something.
Note: Always write the preposition "into" as one world.
355. For and At (Price)
(a) For
(X) I bought a book at fifty dollars.
(O) I bought a book for fifty dollars.
(b) At
(X) I can't buy it for such a high price.
(O) I can't buy it at such a high price.
Use "for" if the actual sum is mentioned and use "at" if the actual sum isn't given.
Note: If the weight or measure follows the price, use "at" with the actual sum.
That velvet is available at $5 a yard.
356. Between and Among
(a) Between
(X) There was a fight among two boys.
(O) There was a fight between two boys.
(b) Among
(X) Divide the apple between you three.
(O) Divide the apple among you three.
Use "between" for two only. Use "among" for more than two.