half-hearted--------不认真的（形容词）

英文释义
(adjective) Having no enthusiasm; lacking interest or energy.

例句
My son practices the piano for an hour every day in a half-hearted manner because he would rather play outside with his friends.
我的儿子每天很不认真地练一个小时钢琴，因为他更喜欢和朋友们出去玩。