@1 soru hatalı.

aslı şöyle bir şey;

A man goes into a shoestore and buys a pair of shoes for $5. He pays
with a counterfeit $20 bill but the shoestore owner does not realize
it. Not having change for the $20 bill, the owner runs to the grocer
next door. The grocer gives the shoestore owner four $5 bills and the
shoestore owner gives the man the shoes and $15 change.

Later the grocer comes back to the shoestore owner with the FBI and
informs him that the $20 bill was counterfeit, so the shoestore owner
gives the grocer $20, and the FBI keeps the counterfeit bill.

How much did the shoestore owner lose?

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ve cevabı da:

You can diagram the situation this way, with C for the counterfeit
bill and S for the shoes:

Buyer Shoestore Owner Grocer FBI
-C ---> +C
-C ---> +C
+$20 <--- -$20
+S+$15 <--- -S-$15
-$20 ---> +$20
-C ---> +C
===

=

==
-C+S+$15 -S-$15 +0 +C

Let's think about what everyone has gained or lost:

The buyer lost a counterfeit bill, and gained a pair of shoes and $15.

The shoestore lost a pair of shoes and $15 (the counterfeit bill just
passed through, and the extra $20 just paid for the 4 $5 bills).

The grocer came out even.

The FBI gained a counterfeit bill.

Technically, the shoestore didn't lose $20, since the shoes didn't
actually cost the store $5. We can't say how much money they actually
lost.

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yani, satıcının ayakkabıyı toptancıdan kaç para vererek aldığını bilmediğimiz için kesin bir cevap veremeyiz. ama 50 liradan daha düşük, 15 liradan daha fazla olduğunu söyleyebiliriz.