Here are three pairs of rods. The ratio of all the pairs is 3 : 2.
What is the ratio of the pair below?
Using only single rods what pair can you find with the same ratio as the pair below?
Using only pairs of single rods what pairs can you find with the same ratio as those below?
Using only pairs of single rods what pairs can you find with the ratio 9 : 6?
Why do this problem?
Cuisenaire rods are a fantastic resource for investigating ratio.
The way the problem is written assumes knowledge of the concept of ratio, but Cuisenaire rods could be used to introduce the ideas initially. Children will find it useful to have some "real" rods to use while working on the problem, and the interactivity can be a good medium in which to engage the whole class in initial discussion, perhaps on an interactive whiteboard or using a projector. White
rods (which are unit length) can be used to demonstrate what exactly a ratio of 3:2 means and there is a lot to be talked about in terms of why 3:2 is the same as 6:4, 9:6 and so on.
The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the
NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to
embed rich mathematical tasks into everyday classroom practice. More information on many of our other activities
can be found here.