"Imprudent" means, basically, "reckless" or "without taking thought". It would be imprudent of you to spend all your money on that car and not save some for your rent.
It means unwise, rash, or indiscreet. Here are some sentences. His imprudent remarks were overheard by his boss. That is an imprudent thing to do. She can make some really imprudent decisions.
The word imprudent means being careless another word for careless would be not showing care. So an easy sentence would be (Sabrina was very imprudent about her science project so she got an f-)