Why pray for something minor like an exam grade?

What makes you think your God will assist you in this when he has stood by throughout history when people being murdered have prayed for their lives have not gotten their's answered, here's some desperate prayers:"Please don't kill me God!", "God save me!". It's obvious a benevolent, omnipotent deity would help someone (and has the power to) who did not deserve death but he just stands by and probably laughs. So Christians which one is it? Either your god is: malevolent, is not all-powerful, or (I like this one) he does not exist.