Solve this if you're smart

No.13613706 ViewReplyOriginalReport
There are two phone bills that need to be paid.
A mother gives his son 2 grand, belonging to an old lady, whilst asking him to add 1 grand of his own into this money pool, letting him know that she'll pay him half of what was spent on their bill.
The boy arrives on the spot. He's asked for both credentials. The lady's phone bill is 770 for one month and 770 for the second, whereas the family's bill is 630.
Now, for the son's part, he pays both of them at the same time with that two grand and half of his grand coming back home with the rest.

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1. What's left of the money pool?

2. How much of the rest needs the old lady be getting paid back for?

3. How much does the mother need to pay her son back?