Helpful Hints for Exams (And for practice on assignments)
1. Say what you're doing.
In the exams, the TA's and I will give you 25% credit for an answer if we can just tell
what method
it is you're using, and an additional 25-50% if it's the right method. You
won't
necessarily get exactly the numerical values given on the model answer
sheets --
in many questions there are several defensible ways of solving the problem.
For
example, in Question 4S.3, you could choose a study period of 20 years, 30
years, or eternity. This all give the same conclusion, but somewhat
different
numbers.
To make it easy for us to mark it right, say what the numbers you're writing
down
are supposed to be, e.g.,
``Present worth of wages = A(P/A,i,N)''
If we're just confronted by a page of anonymous calculations, there's not
much
we can do except glance through it and see if any of the numbers look
anything
like any of the numbers in the model answer.
2. Use explicit conversion factors, i.e., expressions like `(P/A,i,N)'.
Using an algebraic formula instead is more work, and there are many more
opportunities
to make a numerical slip. The only time you should use the formulas is
when
creating a spreadsheet. Even then, it's a good idea to write out what it is
you're
calculating in terms of the conversion factors -- this makes it easy for us
to give
credit even when there's a mistake in the spreadsheet (which can easily
happen).
If you don't have a copy of the text, you can find tables of conversion
formulae
on line, for example at:
http://www.uic.edu/classes/ie/ie201/discretecompoundinteresttables.html
3. Avoid excessive precision.
If you're calculating the present value of a million-dollar investment,
don't bother
specifying it to the nearest thousandth of a cent. Three significant
figures is usually
adequate, and anything after the fifth significant figure is just
imaginative fiction.
When presenting a table of numbers, they should all be given to the same
level
of precision, and the decimal points should align vertically. Let the table
entries
be in thousand-dollar or million-dollar units, so there are only a few
digits on either
side of the decimal point. If you do have more than three digits to one
side of the decimal
point, separate them into groups of 3 by commas or spaces.
4. Answer the question asked.
If the question asks, `` which alternative is best? '', don't just calculate
the value
of each alternative and leave it to the reader to figure it out. Say it
explicitly.
John Jones
Fri, Sept 10, 2010