I had many trials and these are in my opinion the best for an introductory, undergraduate level:
ODEs: Holzner: Differential Equations for Dummies
PDEs: Farlow: Partial Differential Equations for Scientists and Engineers
I had many trials and these are in my opinion the best for an introductory, undergraduate level:
ODEs: Holzner: Differential Equations for Dummies
PDEs: Farlow: Partial Differential Equations for Scientists and Engineers