I bought a caot by ten pounds.

问题描述:

I bought a caot by ten pounds.
还是I bought a caot for ten pound.

I bought a coat for ten pound是正确的!
牛津高阶英汉双解词典220页词BUY的例句:
I bought it from my a friend for $10.意思是:我从朋友那里花了10美元买来的.