"For" and "to" are used the most, but "with" certainly makes sense. Think about the meaning of the word "suited". When a tailor makes a suit for you, you are "suited" with the suit that he makes. So, when you say "he is well suited with this task", it means that the task fits him like a well fitted suit. It is not said often, but the words have meaning and they make sense, so you can say it.

First of all I think Jonathan and Amandi did a great job explaining how "with" could be the correct answer. English grammar isn't like math where there is only one right answer. I agree with you that it makes sense to say: "He is well-suited FOR this task". That is what I would have guessed. If you are well-suited "for" a task you have the ability to do the work. As I thought about the meaning of the sentence "He is well-suited WITH this task" It sounds like he is enjoying his job. He is happy with his job. A task can be tedious for one person, but a fun challenge for another person. You asked a very thought provoking question and that English textbook is challenging you to think through word choices thoroughly. Keep up the good work. To have a "gut" feeling about something is a great step toard fluency. Your use of slang is perfect. I was a little weirded out too, and I had to think why someone would be well-suited "with" a task. Happy studying. You are a great English student and the kind of student this textbook was written for. You shouldn't always take the right answer in the back of the book as the ONLY right answer especially if you think another one sounds good too. All the English listening and reading that you do aside from the book is helping you remember correct grammar structures.

Both "for" and "with" can be used in this context, but they have slightly different meanings. If you say "He is well-suited for this task," it means that he is suitable or well-matched for the task. It emphasizes that he has the skills, abilities, and qualities required for the task. If you say "He is well-suited with this task," it means that he has a good working relationship or partnership with the task. It emphasizes that he can work well with the task and that the task is a good fit for him. Therefore, both prepositions are correct, but they convey slightly different meanings. It's possible that the book you are using is emphasizing the collaborative aspect of the task, which is why it suggests "with" instead of "for."