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