books for EE quals signal and system area

A First Course in Probability
Sheldon Ross
Seventh edition, international edition
very clean, just like new, this book is extremely useful to prepare signal area
asking for $15 or OBO

Signals and Systems
Oppenheim
2nd edition, international edition, paperback
very clean, like new, this book is very useful to prepare system area
asking for $20 or OBO

Signals and Systems (2nd Edition) solution book
like new, paperback
asking for $20 or OBO

Probability and random processes for Electrical Engineering
Alberto Leon-Garcia
Second Edition, international edition, paperback
like new
supplementary book for signal area
asking for $10 or OBO