Calculating percentage increase and decrease
Calculating percentage increase
Calculating percentage increase is an important skill for geographers to have. When geographers collect data over a period of time the results may increase. Calculating a percentage increase allows a geographer to see how much their data has changed. For example, it may be useful to find out how much the width of a river channel increases as you travel downstream.
- work out the between the two numbers being compared
- divide the increase by the original number and multiply the answer by 100
- in summary: percentage increase = increase ÷ original number × 100
For example, the number of robins in a woodland area is counted over two different months. In December 15 robins were counted. In January 23 robins were counted. What is the percentage increase of robins in the woodland?
- the difference between the two numbers is 8
- 8 ÷ 15 × 100 = 53.3
- the percentage increase of robins found in the woodland is: 53.3%
Calculating percentage decrease
Calculating percentage decrease is also a useful skill to have. For example, it may be useful to find out how much the particle size decreases in a river as you travel downstream.
- work out the difference between the two numbers being compared
- divide the decrease by the original number and multiply the answer by 100
- in summary: percentage decrease = decrease ÷ original number × 100
For example, the number of robins in a woodland in February and March is counted. In February 22 robins were counted. In March 12 robins were counted. What is the percentage decrease of robins in the woodland?
- the difference between the two numbers is 10
- 10 ÷ 22 × 100 = 45.4
- the percentage decrease of robins found in the woodland is: 45.4%
