Why is the remaining credit positive?

Question

Maybe it is wrong equation:

-7.1 + 1.63 = -5.47   #instead of +5.47

Why does the seller say -7.1 + 1.63 = 5.47?

Answer 1

This looks like a summary of a credit card statement. Assuming that, then this equation is of the form

money you owe us already + new spending you owe us from this month = total you owe us now

In this case, the starting balance is actually a credit (negative debt; likely you overpaid your previous bill, or some charge got refunded), and is therefore expressed as a negative number. The additional charges this month get added to that to calculate the new amount owed, which is -5.47; this is another credit (you owe a negative amount of money, or, in other words, they owe you).

However, the presentation of the numbers is inconsistent. The starting balance is listed as how much you owe them; this happens to be a negative number. The ending balance, if expressed as the amount you owe them, is also a negative number. But they have chosen to present it differently in this case, as a credit. The meaning is the same.

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_{If this is not a credit card, the main point(s) of this answer likely still apply}

Answer 2

This is a UI feature. And a very important one!

A recurring problem in the 80s was credit card bills would arrive with a return envelope and payment slip showing a $4 credit balance. So when shuffling through the monthly bills, many citizens would write a $4 check and stick it in the envelope with the slip. Due to the high volume of payment processing, it was impracticable to pop it out and politely return the check - anyway citizens sometimes overpaid credit cards to have room for a purchase which exceeded their credit limit. Next month, they'd receive a bill with a return envelope and a $8 credit balance. Guess what they'd do. This would snowball.

So credit cards have iterated on changing the UX to feature the credit balance in a more bold and distinctive way. For instance, some rigged their auto-stuffers to omit the return envelope.

As such, they have a long history of "stating it clearly so the accounting novice does not miss it" as a much higher priority than accounting exactness.