If we have an exam we should study. Can we study for exam instead of reading Holy Qur'an or should we say our prayer very quickly for the sake of exam?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Reciting Qur'an is among the excellent forms of worship and one gets much reward for this deed.  The Prophet (Sallallahu Alaihi wa Sallam) said: "Recite Qur'an since it comes as intercessor for those who recite it." [Muslim]

Imam al-Tirmizi narrated from Ibn Masoud that the Prophet (Sallallahu Alaihi wa Sallam) said: "Whenever a person recites one letter from the Book of Allah, one good deed is recorded for him. One good deed is equal to ten good deeds the like of it. I do not say that Alif-Lam-Mim (that's the first word of the 2nd Surah) is a letter, but "A" is a letter "L" is a letter and "M" is a letter."

Sheikh al-Al bani graded it as Sahih.

If the study you are busy with is lawful and beneficial for you in this and the next life then the study itself, and preparing for exams all become a form of worship. Study helps you get a suitable job that can prevent you from asking others or taking things from them. It helps you cover the expenditure of your wife and family members which is a duty of a Muslim.  The Prophet (Sallallahu Alaihi wa Sallam) also said: "And (know that) whatever you spend in Allah's Cause, you will get a reward for it, even for the morsel of food which you put in your wife's mouth."

The prophet said: "No one ever eats better food than what he has earned from his own hands. Indeed the Prophet Dawood (Alaihi Salaam) used to eat by working with his hands."

However, you have to concentrate on your studies as much as possible along with making Du'a that Allah grants you the good of both lives, this life and the Hereafter.

Turning away from using the means that are permitted in Shariah is against Islamic Shariah.  Sheikh al-Islam Ibn Taymiyah wrote in his Fatawa: 'Dependence on means is a kind of Shirk, denial of means is a deficiency in mind and giving up the lawful means is defaming the Shariah.'  So, a person should always heed to Allah and depend on Him not in the worldly means.  Allah provides him the means that suits and benefits him.

If the means are achievable then one is ordered to use them along with having trust in Allah as he performs the obligatory prayers, makes Jihad against enemies, uses weapons, and wears armor, etc.  It is not sufficient to give up all that he can do only by trusting in Allah to defend him against His enemies without making Jihad against them.

The Prophet (Sallallahu Alaihi wa Sallam) said: "A strong believer is better and is more lovable to Allah than a weak believer, and there is good in both, (but) cherish that which gives you benefit (in the Hereafter) and seek help from Allah and do not lose heart, and if anything (in the form of trouble) comes to you, don't say: If I had not done that, it would not have happened so and so, but say: Allah did what He had ordained to do and (know that) your "if" opens the (gate for the Satan)."

Allah knows best.