I borrowed the money at 5% interest.
二.interest當興趣用時既有可數名詞又是不可數名詞，
看具體表示什麽意思，例如下面的幾種用法：
1. 興趣;關註;愛好
I developed an interest in the machine.
我對這機器發生了興趣。
I have lost my interest in chemistry.
我對化學已不感興趣。
2. 趣味性(+to)
Local color added interest to the novel.
地方色彩增加了這部小說的吸引力。
3. 感興趣的事物或人（這是就可數）
His two great interests in life are music and painting.
三.股份,股權(+in)]
He has an interest in the company.
他在這家公司擁有股份
四. 利潤，福利，利益，好處
He always puts the interests of the people before his own.
他總是把人民的利益置於個人利益之上
希望能幫到妳，祝更上壹層樓O(∩_∩)O