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If I borrow from two of my parents 50 dollars and spend 45 dollars at the store, I am left with 5. On my way home, I borrow to my friend 3, now I am left with just 2. I return home and give 1 to my dad and 1 to my mom, so I owe them 48 in total. And my friend owes me 3...so in total it becomes 51 and not 50 it used to be at the start. What is it? Anyone has explanation to this? Thank you. (sorry about the tag, couldn't figure out where to put it)


marked as duplicate by Jyrki Lahtonen Sep 2 '15 at 8:12

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  • $\begingroup$ You'll find your answer once you (try to) precisely define what "it" is. $\endgroup$ – David Mitra Feb 2 '15 at 11:05
  • $\begingroup$ You could just as well say that you owe your parents $45 and your friend owes your parents $3. $\endgroup$ – Mattos Feb 2 '15 at 11:09
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    $\begingroup$ I think it's called bad accounting. You should subtract your debits from your assets. Currently your balance sheet is $3-48=-45$ (you expect $3$ from your friend, but you owe your parents $48$). $\endgroup$ – paw88789 Feb 2 '15 at 11:10
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    $\begingroup$ Not again :-( ${}$ $\endgroup$ – Jyrki Lahtonen Sep 2 '15 at 8:12

This is called a sign error, which happens very frequently in hand computation. It is combined with a failure to write down the proper right hand side, which augments the confusion.

The non-equation you write down is $$ 48 + 3 \neq 50 $$ where the $48$ is what you owe, the $3$ is what is owed to you, and the $50$ is irrelevant to the problem. The equation you should have is $$ 48-3 = 45 $$ where the $48$ is what you owe, the $3$ is your credit on behalf of your friend; it can be combined with oyur debit only after changing the sign. The left hand side is now your net debit. The right hand side is the value of what you bought, which matches your debit since you did not provide any of the money from your own resources.


It is a good idea to study accounting. :) Here is a little course on accounting.

An account:

An account is a big T with a name referring to an entity you do transactions with.


When you do a transaction with an account then you do a posting. The posting describes the transaction in the language of accounting.

Action of the first kind:

If you take out money from an account then you write the amount to the right side of the T. (In red for now, red meaning a negative number, an amount you owe to the account.)

Action of the second kind: You put money into the account. Then you write the amount to the left side of the account. (In black, meaning that the account has swallowed your money.)

Posting again:

Every transaction requires two actions (first kind and second kind): You register where the money came from, and you register where the money went to.

I did the accounting based on your story. You can identify the postings.

The balance sheet shows that there is no problem.


Why add the 3 that your friend owes you to what you owe your parents? You should subtract it. Go get the 3 back from that leech you call a friend, and give it to your parents. Now you only owe them 45, which is what you spent at the store. You probably spent it on root beer, so you'll need to get a job to pay them back what you owe them.

Hope that helps. :D


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