3 beggars have 10 pence each. The local cafe is offering 3 cups of coffee at the collective price of 25 pence (just for beggars!). None of the beggars have change, so the waitress offers them 1 pence each in return and keeps 2 pence for herself.
Now, in effect, the three beggars have paid 9 pence each for their cup of coffee. And 3 X 9 = 27 pence. + 2 pence that she kept and you have a grand sum of 29 pence…
Is this how accountants fiddle books (not that they would, of course)?

By switching a minus sign for a plus sign? Yes, I’m sure that’s one of the standard techniques for fiddling with calculations.

If you’re asking why they don’t add up, the beggers paid a total of 27 cents, 2 cents went to the waitress, 25 cents to paying for the coffee. No mysteries there.