The maths required for an economics degree I have a degree in computer science and I wanted to do another degree in economics.
However, my maths have been weak since high school always scoring slightly above passing rate. During my course of study in computer science I have score 60 marks for my maths module (which covers probability, differential equations, mainly on discrete maths topic).
I would like to revisit my high-school and undergrad maths module to prepare myself. 
I have found some free online learning materials at: http://rutherglen.science.mq.edu.au/wchen/ln.html
What are the modules should I revisit to improve on my foundations?
 A: If you are doing an undergrad degree, then you likely will need more applied math classes.
You might see classes like algebra, calculus, finite math, business math, differential equations, linear algebra, probability, statistics, complex variables, real analysis, numerical analysis and the like. You might also be required to take some programming courses.
If you are doing a graduate degree, then you likely need more theoretical classes.
Here you can see courses ranging all the way up to game theory, calculus, differential geometry, differential equations, topology and the like.
If you have a particular school in mind, you should certainly look at their requirements and maybe talk to a counselor. 
You should also check out some of the wonderful Opencourseware, for example, at MIT.
Lastly, you certainly want to visit your local universities and look at the course requirements and the books in the library.
A: I've just finished an economics degree and am now finishing an applied mathematics degree. My answer is based on personal experience but my experience is, more or less, roughly equivalent to the experience of most economic undergraduates.  
Most schools will offer some sort of "calculus for business majors" that generally satisfies the mathematical demands of undergraduate level economics. However, a solid course in Cal. 1 certainly won't hurt.  
Examples of calculus in economics might be using simple derivatives when working with production functions to ensure the production function satisfies Inada conditions, determining the marginal product of labor or the marginal product of capital.  
The undergraduate level economics courses are designed to develop a solid understanding of the logical impetus of economics. You will use some math, but that math will serve the purpose of reinforcing economic ideals. Attending a top tier school might greatly undermine the validity of this advice. For example, I think Columbia undergrads need concepts from Cal. 1 and Cal. 3 during their course work.  
Be prepared to learn and apply statistics while studying economics, FYI. Especially if you plan to study econometrics.  
IF YOU WANT TO GO TO GRAD SCHOOL! You will need a much more robust understanding of mathematics.  You should consider completing multivariable/vector calculus, linear algebra, differential equations (ODE at least), analysis and possibly a proofs course.  
Hope some of this helps.  
A: I would say the most important are multivariate calc, particularly constrained optimimization, linear algebra, and statistics.  I agree with Amzoti that if your goal is grad school, more theoretical work is needed, at least real analysis.  There are quite a few "math for economists" books, such as Glaister's Mathematical Methods for Economists.  Use the books themselves or to get an idea of the topics needed.
A: I am a double major in mathematics and economics. Here's what helps:
Undergraduate degree in economics: calculus and an upper-level statistics course. If you really want to impress your professors with research, I highly recommend taking multivariate calculus and differential equations. Linear algebra is not necessary, but it will make life a lot easier. Fortunately, you don't need to be incredibly math-oriented to succeed in these courses (but they will make math addictive). 
If you're looking to study economics in college but you'd also like to go on to graduate school, then it's vital that you take multivariate calc, differential equations, linear algebra, probability, statistics, mathematical modeling, and real analysis. In fact, many top economics schools will just check to see how you did in real analysis and calculus before looking at other grades. 
If you're going for a graduate degree in economics, you'll most likely take partial differential equations, probability & statistics, real analysis, and maybe even stochastic processes, depending on what your area of research is.
The more mathematics you take for your economics major, the better quality your research will be; the better quality your research is, the easier it will be to be accepted into a graduate program in economics. 
If you're not interested in academia, then taking a statistics course and calculus 1 should suffice. 
