Question: Assalamualaikum.i am a student.I am currently preparing for an exam.It is very tough for me to pass the exam and obtain a good rank.But I am trying my level best and studying very sincerely.Can you suggest me any Dua which will be answered quickly by Allah and which is such effective that I will be able to pass the exam??

Answer: 
Calm down. Your O and A levels will do nothing to your life. What's written is written. If you are meant to live in a lesser house, drive a lesser car, then your A\* in your exam can't change it.

Finally, the dua, doesn't have to be specific words. Just ask Allah to make it easy for you.
For an Arabic dua in particular, read this:

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> اللَّهُمَّ لاَ سَهْلاً إِلّاَ مَا جَعَلّتَهٌ سَهْلاً وَأَنّتَ تَجّعَلَ الحَزَنَ إِذَا شِئتَ سَهْلاً (See [here](https://sunnah.com/hisn/140) with transliteration)
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You can make dua but it may not be accepted/what you ask for may not be given to you. Your dua will be acknowledged. Focus on your exams but also in your duties in Islam. Praying and whatnot.