Text

In 2020, a country had approximately 100,000 hectares of forests. Every decade, it is estimated that the number of hectares of forests will decrease by 20%. In order to slow down this deforestation, a non-governmental organisation (NGO) has decided to plant 3,000 hectares of trees every decade.

1. How many hectares of forests will there be in 2030? 2040?
2. Here is a function written in Python ($n$ is the number of decades):
   

     
   def forest(n):
       h = 100000
       for k in range(n):
           h = h * 0.8 + 3000
       return h
     
     

   1. Explain the algorithm.
   2. Run the algorithm step by step for $n = 3$
3. Complete the following algorithm to find the year when the number of hectares of forests will go below 30,000 for the first time. Explain.
   

     
   def year():
       n = 0
       h = 100000
       while h ...
           n = n + ...
           h = ...
       return 2020 + ...
     
     

Audio

Version 1 (Marianne Haziza) ??

Version 2 (Alice Rallo) ??

Vocabulary

• decade: a decade is ten years