Money is written in pounds and pence. There are
100 pence in a pound, so \pounds 1 = 100\text{ p}. An amount
like \pounds 3.45 means 3 pounds and 45 pence —
the two digits after the point count the pence.
Because money uses two decimal places, you add and subtract amounts of money just like any
other
decimals:
line up the decimal points (pounds under pounds, pence under pence), then
work column by column. For example, \pounds 2.30 + \pounds 1.45:
2.30
+ 1.45
------
3.75
So \pounds 2.30 + \pounds 1.45 = \pounds 3.75.
When you pay for something with more money than it costs, the shopkeeper gives you
back the difference. That is your change:
\text{change} = \text{amount paid} - \text{cost}
A toy costs \pounds 6.40 and you pay with a
\pounds 10 note. Lining up the points (pad
10 to 10.00):
10.00
- 6.40
------
3.60
Your change is \pounds 3.60. A handy trick is to
count up from the price to the cash you handed over: from
\pounds 6.40, add 60 p to reach \pounds 7,
then \pounds 3 more to reach \pounds 10 —
that is \pounds 3.60 in all.