To what extent is a student's supplication to achieve first rank for a scholarship answered, and do sins affect the forgetting of knowledge?

Avoiding sins is a reason for preserving knowledge. Supplication (Du'a) can be answered, for Allah is near and responsive to whoever supplicates to Him with sincerity, as long as one does not supplicate for a sin or cutting off ties of kinship, or impatiently seek a swift response. Allah answers supplications in one of three ways: by granting the request quickly, or by storing it for the Hereafter, or by averting an equivalent evil. If the request is not granted, perhaps the good lies in what was withheld, for "IT MAY BE THAT YOU DISLIKE A THING AND IT IS GOOD FOR YOU; AND IT MAY BE THAT YOU LOVE A THING AND IT IS EVIL FOR YOU. ALLAH KNOWS, AND YOU DO NOT KNOW."