Probability Lesson 4: Plenty More Fish in the Sea

Australian curriculum number (ACMSP144; ACMSP145; ACMSP146)

Lesson abstract

Students gather data about a population by sampling. They start in a whole class introduction with a small set of unseen counters in a bag and work out the proportion of colours in the bag by sampling and replacing. ‘Tagged fish’ are introduced into the bag so that the numbers of counters in the bag can be estimated.  This method is then applied to estimate the population of the school playground by releasing students as ‘tagged fish’ at break time. 

Mathematical purpose (for students)

To learn how the size of populations can be estimated. 

Mathematical purpose (for teachers)

Students engage in a practical experience of the important capture-mark-recapture method of estimating animal populations.  In doing this, students apply the central idea of reSolve lesson 30 300 3000 that the probabilities related to a whole population can be estimated by the relative frequencies (e.g. percent frequencies) calculated from a good sample. 


At the end of this lesson, students will be able to:

  • Use sampling to estimate the composition of a population.
  • Recall the importance of sample size when collecting data.
  • Appreciate one way in which mathematics is used in environmental science.