21. Necesito comprar un coche. Yo te doy mil dólares POR el tuyo.
Por is the correct answer. But I do not know why. I was taught that you always used para as a destination. Is por the correct answer because I am giving you the $1000.00 in exchange for your car?

Question

21.	Necesito comprar un coche. Yo te doy mil dólares POR  el tuyo.
Por is the correct answer.  But I do not know why.   I was taught that you always used para as a destination.  Is por the correct answer because I am giving you the $1000.00 in exchange for your car?

Answer

"por" and "para" have several uses. In this case "por" indicates change. Check this link to know all the uses of "por" and "para"
http://roble.pntic.mec.es/~acid0002/index_archivos/Gramatica/preposiciones_por_para.htm

Answer

exactly.  we use POR always I am giving you and you are giving me. It´s a change.

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