Needed help in learning modular arithmatic

I have trying to learn modular arithmatic by solving various problems such as power series sum with modulo and other similar kind of problems involving algebra,combinatorics and modular arithmatc,but getting stuck in every next problem i have been solving.Can someone suggest is it the right way to proceed.
If it is then suggest some problems to solve in sequential order.
If not then please suggest some learning resource.
Thanks in adv!.

I would say keep practising the problems with the above tags on codechef.

I think some important formulas which might help you are:


And the most important one


This can be written as (Using fermats little theorem)

    (a/b)%m=((a%m)+((b^(m-2))%m))%m (Using little fermats theorem provided m is prime)

Some resources

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I think this can help

Have you done the theory first?