How can i convince my mom to get me a ps3?

ok here is all i know. so i am moving to a new house this december. but first i have to sell my house and my grandmas house so that we can live all together in one house. but my mom says it might be a little hard to sell my grandmas house so we might have to live in my grandmas house for a couple of months. My grandmas house is so boring. there is no cable tv and no stuff to do. so i ask my mom if i can get a ps3 so that i can solve my boredom when i move. also my birthday and Christmas and thanksgiving is pretty close to each other so i get alot of money. i mean A LOT. i get about 400 dollars every holiday. so i say ill pay for everything but my mom says that i need to be in the honor roll. but i dont think that i can be in honor roll because the grade average has to be over 95%. so how can i convnce my mom!!