# Measurement (area & perimeter): Shrinking Lakes

## The Problem

There are 3 Lakes – Lake Moshi, Lake Nagoo and Lake Drogo. You can see each lake’s size and shape on the graph paper opposite. Sadly, the lakes are decreasing in size due to climate change and other human-made factors.

The rate by which each lake is decreasing in size are as follows:

• Lake Moshi – 2 square kilometres per year
• Lake Nagoo – 4 square kilometres per year
• Lake Drogo – 3 square kilometres per year

Which lake do you think will be the first to disappear? Why do you think that?

Do any assumptions need to be made when calculating the first lake to disappear?

Did you know?

The Aral Sea in Central Asia was once one of the world’s largest lakes. In half a century, this ancient lake has almost completely disappeared – leaving behind a salty desert. Irrigation for farming and global warming are the main causes of the lake’s destruction.

## Visualising the Problem and Getting Started

Molly said, “Lake Nagoo will be the first lake to disappear because the rate at which it is decreasing each year is greater than the other two lakes.”

Do you agree with Molly’s reasoning?