# Obtaining a given resistance through series and parallel combinations

• ELEN_guy
In summary, an EE student is trying to find a solution to an assignment involving series and parallel combinations of resistors. They found two solutions using simple formulas, and are looking for help from others who may know more about the algorithm for this type of problem.

#### ELEN_guy

Hi, just joined this forum, I am an EE undergrad and trying to find a solution to the following assignment, hope somebody here could help or point me in the right direction.

Given some resistor values (1.8ohm, 20ohm, 300ohm, 24kohm, 56kohm) I must construct series and parallel combinations that will give the following equivalent resistances: 8.5ohm, 161ohm, 12.17kohm, 96kohm.
Its also best if the smallest quantity of resistors are used to construct these circuits.

Ive been randomly trying different combinations but this must be done routinely in the field so there must be so rigorous algorithm to achieve this, right?
If anyone knows how this is down or perhaps knows a site with a tutorial on how to do this I would be very grateful.
Thanks.

I've never heard of an algorithm for this sort of thing. You just have to use simple formulas for series and parallel combinations to figure this one out.

Although this would make an interesting computer program. I'll probably try working on something for situations like this when I have more time.

I actually tried writing a C++ program to do this but having only taken one intro level course it was too big an undertaking to be worth the effort.
So I just have to randomly fiddle with the numbers? Is this how its really done in the industry?

Well, I'm still an undergrad, and if I had to get the given resistances using those resistor values, the only I'd do it is by using simple series and parallel formulas.

I know two basic configurations which will allow you to achieve any resistance:
1. T-connection (3-resistors)
2. Pi-connection (4-resistors)
So may bee that is what you're being asked to do? Develop equations for achieving given resistance using well-known matching networks. This will be pretty handy when you start dealing with problems that involves matching a given circuit to another circuit for maximum power transfer.

Last edited: