worth 不可单独作谓语（It is worth doing sth 除外）
worthwhile=worth while 可以单独作表语.
如：
这个问题值得考虑
The problem is worth considering.(不用worthwhile)
It is worth considering the problem.(可换用worthwhile)
It is worthwhile to consider the problem(不用worth)
To consider the problem is worth while (不用worth)
Considering the problem is worth while (不用worth)