A joke for a Key?

"

TreXiD wrote:

"

Reelix wrote:

Person A: X
Person B: Y

"I place $20 into a box."
Person A: X - 20
Person B: Y
I sincerely hope you're joking.
"So do you."
Person A: X - 20
Person B: Y - 20

"There is now $40 in the box." - Correct

"I sell the box to you for $30."

Person A: X - 20 + 30
Person B: X - 20 - 30 + 40

"We both walk away with a $10 profit."
Person A: X + 10 ($10 Profit)
Person B: Y - 10 ($10 Loss)

I sincerely hope you're joking