Authentic Assessment

Bridge Construction

Topic - Algebra - Patterns and Functions

Task - Constructing Bridges


An engineer wants to know how to calculate the number of spans and supports needed for any length bridge constructed using either of the following two designs.

Designs One:

  1. Spans are yellow rods
  2. Supports are red rods
  3. This bridge design is build by adding supports and spans as pictured above to span any required length.

Design Two:

  1. Spans are black rod
  2. Supports are light green rod
  3. This bridge design is built by adding spans and supports as pictured above to span any required length.


Describe how you would calculate how many rods would be needed to build either type of bridge for any possible size. It is okay for a bridge to extend beyond the desired length by part of a span.



(1993). Measuring UP: Prototypes for Mathematics Assessment.
Mathematical Sciences Education Board National Research Council.
Washington, DC: National Academy Press.


Dr. Robert Sweetland's notes