# Math trick – scamming via money-math (most people don’t understand it)

“A question for math teachers or lovers.
There was a boy he wants to buy a T-shirt and the T-shirt was 97 birr. Then he goes to his father and mother and asks to borrow him some money. And then mother gives him 50 birr and father too(50+50=100birr). After taking the money he bought the T-shirt then the cange was 3 birr and now he give 1birr to the mother and 1 to the father now he has 1 birr only. But he need to pay 49 birr for each of them(50-1=49). So, lets add 49+49=98 and the money which he has is 1 then 98+1=99. Where is 1 birr?”

He owes them 97 no matter how you slice it.

He wants to keep the 1 birr for himself, so he’s using slight of hand trickery to keep it. A type of shell game. We used to encounter this in New Jersey (USA) growing up at local gas stations. [in Florida here, we pump our own gas, so I don’t see it at the gas stations here, but in NJ they had to pump it for you]

Let’s say the attendant owes you \$17. They give you back a \$5 and \$2 singles. Then they “realize their mistake” and take it back, exchanging the \$5 and \$2 for a \$10 and \$2, keeping the \$5 for themselves. Sometimes they’ll do this several times, involving the same cognitive flaw most of us have with this type of money math. Supermarkets use this trick all of the time.

You don’t simply add together liabilities if you’re holding onto an asset. Money math isn’t just + and -. Even that is oversimplifying it.

Great question by the way. I enjoyed the challenge smile emoticon

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• birr (32.25 KB
10.10.2015
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