Bob is a student but Carol is not.    Sb & ~Sc
Everyone is ambitious.   (x)Ax
No one is working hard.   (x)~Wx
There are ambitious students and there are students who do not work hard.    (Ex)(Sx & Ax) & (Ex)(Sx & ~Wx)
Every student is ambitious.    (x)(Sx -> Ax)
Some students are not working hard.    (Ex)(Sx & ~Wx)
If all students are ambitious then Bob is ambitious.    (x)(Sx -> Ax) -> Ab
Everyone who works hard is ambitious.    (x)(Wx -> Ax)
Only those who are ambitious work hard.    (x)(Wx -> Ax)
Only those who work hard are ambitious.    (x)(Ax -> Wx)