Multiplying People Statistics In Your World 
Student Notes
Teachers Notes
Rules of the Game
 
Not-so-dirty Rats
 

Generation Game

The Rules of the Game
You will need pages R2 and R3. Scientists are worried that the lovable little furry creature, the 'dirty rat' (Rattus filthicus) is dying out. A careful study of their life-cycle was made.

This showed:

  1. One-fifth of the rats die on their first birthday.
  2. One-fifth of the surviving rats die on their second birthday.
  3. All rats surviving then die on their third birthday.
  4. The female always gives birth to one male and one female rat at the beginning of her second year of life.

There are only 750 rats left. (250 baby rats, 250 rats between 1 and 2 years old and 250 between 2 and 3 years old; there are equal numbers of each sex in each group)

When the total population falls below 300, the rats give up in despair and become extinct. You are going to find the year when they all die off!

Table 6 on page R2 starts to show the number of rats in each age group every year for the 10 years.

  1. Complete the table for the first six years.

Figure 9 on page R3 shows the population pyramids for the first three years.

  1. Draw the population pyramids for the next three years.
  2. Draw a graph to show the total population each year. Use a scale of 1 cm to represent 1 year along the bottom. (Make sure that your scale on the bottom goes along to 12 years.)
  3. Now make a projection for the year in which the rats become extinct.

You can cheek your projection by continuing Table 6 until the total population falls below 300.

 

*Not-so-dirty Rats
The dirty rats decide to improve their public health. As a result fewer rats die at the end of their first and second years. Play the generation game with different birth and death rates to see how they affect population changes.

 

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