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let
lao ban has (x$) + good(21$)
customer has (z$)
laoban's fren has (y$)
the customer buys good from laoban, he pays laoban 100 fake $ = he pays laoban 0 $, he got 79$ and the good(21$)
so the customer got : z$ - 100 fake $ + 79 + good(21$) = z$ - 0$ + 79$ + 21$
= z$ + 79$ + 21$
= z$ +79$ +( 3+ 18)$ --->18 is the cost of good
laoban got 100fake $ = 0$ and he gave the customer the good and he exchanged 100fake money with laoban's fren
so laoban : x$ + good(21$) + 100fake $ - good(21$) - 100 fake $(gives to fren) + 100 $(from fren) - 79$(to customer)
= x$ + 100$(from fren) - 79$(to customer)
= x$ + 21$ (balance)
laoban's fren got 100 fake $ and gave laoban 100$
so laoban's fren : y$ + 100fake $ - 100 $ = y$ + 0$ - 100$
= y$ - 100$ (balance)
finally, laoban returns 100 $ to laoban's fren
so laoban : (x$ +21$) - 100$ = (x$ + 21$) - 21$ - 79$
= x$ - 79$ (final balance)
the laoban's fren gets back 100$ : (y$ - 100$) + 21$ +79$ = y$ - 100$ +100$
= y$ (no change)
so, laoban's final balance = x$ - 79$
compare with laoban original balance = x$ + good (21$)
= x$ + 18$(cost of good) +3$
therefore,
final balance - original balance
= (x$ - 79$) - (x$ + 18$ + 3$)
=-100(included profit), -97(excluded profit)
p.s :cannot type chinese |
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