Imagine you have two bank accounts, one with a balance of £100 in it and a second account with a balance of -£20.
If you combined these into a single account the balances from each would be added together and you would have a total balance of £80. (This is the
same balance you would have had if you had just withdrawn £20 from your first account.) This illustrates rule 1:
Adding a negative number, is the same as subtracting a positive number of the same magnitude.
If your account has a balance of -£50 and your bank manager kindly agrees to "write off" your debt. i.e. to remove the balance of
-£50, this would leave you with a balance of £0. (If you had deposited £50 into your account, this would have achieved the same
result). This illustrates rule 2:
Subtracting a negative number, is the same as adding a positive number of the same magnitude.
In the above examples, once you have applied either of the rules to rearrange the sum, you are left with a simple familiar
calculation. However this is not always the case and you may be faced with several possible unfamiliar procedures.
you may be required to:
The next page shows how to deal with these situations.