As a parent, if my kid asks for an expensive laptop, I'd be thinking, "What's in it for me?" Then it dawns on me: make 'em earn it by doing more chores.
If you want to convince your parents to spend money on you, you need to show them the benefits of doing so. Get good grades, help a round the house, in short be the kind of son parents brag to other parents about. Do that and they'll get you anything. Heck, I'd get my boy a top of the line MBP even if it meant selling a kidney.
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Not mine, of course.