Making only Du`a’ to Obtain Good Results in the Exams

asalamualaykum. i have just recently finished my exams and will be going to college in september inshallah. i have had a question that has been on my mind for a while now. i have a couple of friends approximately 6 who are all also muslim, the problem is though that they dont act like muslims. they do very sinful acts like drinking, smoking drugs and getting very friendly with girls. they are all aware that these are sinful acts but do not stop. their parents do not know. befor my exams had started i worked very hard in my studies and prayed and made duas to make the exams easy for me. my friends however, they didnt pray and make dua and just carried on with the sinful acts. however, when it comes to exams they do not have to revise and work as hard as i do, but then when the results come the achieve the top grades with out making dua and praying, also they do not study as much and still achieve the top grades. now recently i have just done my important exams and made lots of duas for the exams to make them easy for me, but i found them difficult and i have a feeling i will not do very well. i cannot understand why this could happen as my friends who do the sinful acts and never pray, they found the exams very easy and they are not worried about the results they will get. and i think they will achieve the top grades. can you please explain to me why this is. alhamdulillah i know my rights and wrongs in islam and i try to stay away from sinful acts but i cannot understand why some one who is embarassed to pray and be a muslim still achieves the top grades and gets into the top colleges without making duas. is there specificly any duas i can read until my exa ms restuls come? Jazakullah for your time and effort.

Du`a’ and Qadar

As salaamualaikum wa rahmathulaihi wa barakathuhu May Allah bestow his blessings and mercy upon you for guiding those in need.My question relates to Qadr or predestination in Islam. It is a belief that dua can to an extent change and influence a persons predestined path of actions. My question relates to marriage. I?m currently in a relationship with a woman and things aren?t looking too good for us in terms of getting married due to vast cultural differences. We are praying hard that things work out and we do get married. My question is that if we do ask dua and if Allah does will for us to get married then is it in some way gonna affect the way our destinies should have been and cause a big change in out futures for some reason. Also we are asking dua because we are in a relationship which is not allowed in Islam in the first place and if we do get married then will it in any way bring in a bad affect to our marriage if we were predestined to be with someone else.My second question is that if marriages are predestined and being in relationships is wrong then how would Islam explain a couple in a relationship who go on to get married. Would they have found each other and gotten married anyway.Finally if dua can change a persons predestined path of actions then does a person who asks a lot of dua in someway decide his own destiny, maybe not at everything but some major aspects which may have a big impact on his future.If the best thing in pleasing Allah is ending this relationship I would appreciate some advice on how best to do it. Jazak Allah Khair.