Microsoft Office Tutorials and References
In Depth Information
Calculating the quantities
When you enter that, you see the value 5 go into the cell, which is half our trip
length. So what about our petrol budget? This is also calculated per day. If you
thought the right answer was to use the same formula as the one used for car hire,
award yourself half a point. For the full point, you need to take a different approach.
The size of the petrol budget actually depends on the number of car hire days
more than it does the length of our holiday, so you should base the calculation for
the petrol budget on the number of car hire days. In cell D8, which represents the
number of days of petrol you need to budget for, enter the formula:
=D7
This takes the number of car hire days from cell D7 and puts it into the cell for the
number of days a petrol budget will be needed. The numbers on screen are the
same as they would have been if we’d reused the same formula, so why make a
distinction? It’s because it makes the spreadsheet more ﬂ exible. What if, later on,
we decide to rent a car for the whole holiday? By doing the formula this way,
we only need to change the number of car hire days and our petrol budget will
update automatically. Similarly, we can take out all car related costs by setting
the car hire days to zero. If we had calculated our petrol from the number of
days, we would have to update that formula too, whenever we changed our car
hire formula.
The art of creating good spreadsheets is partly about working out relationships like
this. It’s not always easy, but the more speciﬁ c you can be about describing how
numbers relate to each other, the more reliable your spreadsheet will be. I’ve only
got six rows on my spreadsheet, but your full holiday budget might run to 20 rows
or more. If you need to change two things to reﬂ ect one decision, there’s always a
possibility you might introduce inconsistencies or forget to update something,
which will throw your sums out.
You can also use the mouse or cursor keys to indicate cells you want to use
in a formula. Enter the equals sign into a cell then either click on another cell
or use the cursor keys to move around to the cell you want. Press Enter and
its reference will come up in the formula.

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