I AM NOT TAKING ANY INTERNS
If you are interested in probability you might want to look at the following book and two course web-pages, especially the homework and quizzes :
https://www.isibang.ac.in/~athreya/psweur/
http://math.iisc.ac.in/~manju/UGstatprob18/statprob2018.html
http://math.iisc.ernet.in/~manju/ProbModels/Probmodels.html
The reference books - Pitman and Sheldon Ross - are probably the best suited ones.
A little more advanced is the book of Meester.
For practice problems in basic mathematics (Linear Algebra, Analysis, Probability and Statistics), please see https://www.isibang.ac.in/~athreya/swms2018f/
For additional reading, please see https://www.isibang.ac.in/~athreya/swms2018f/#smrd
Also for more advanced topics in probability, see http://math.iisc.ernet.in/~manju/suggestedreading.html
For various other courses, please see the following pages for reference books as well as question papers for some practice problems. Some books that I recommend to for an introduction to other basic mathematics courses are :-
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Analysis - Bartle and Sherbert : Introduction to Real Analysis
Linear Algebra - A. R. Rao and Bhimasankaram : Linear Algebra ; G. Strang : Applied linear algebra
Algebra - S. D. Dummit and M. R. Foote : Abstract Algebra.
Topology - G. F. Simmons : Topology and Modern Analysis.
Complex Analysis - D. Sarason : Notes on Complex Function Theory.
Differential Equations - G. F. Simmons : Differential Equations : Theory, Technique and Practice ; W. Boyce and R. C. DiPrima : Elementary Differential Equations.