(1) It is like this. Allah decided for 3x rizq for whole life time. For fifty years he was given x. Allah knew that he'll ask for more after fifty years. So for next fifty years he was given 2x. Total will be 3x in hundred years-if his life extended to hundred years. There is the related issue of determinism versus free will. Please read and reread the translation of Verses 81.27-29 together with comments number 5995 and 5996 by Abdullah Yusuf Ali to get this cleared. (2) We know that Supplications (du'a) can even change the destiny. Wassalam