Playing With Percentages

Here are some examples of the sorts of calculations mentioned in the video.

Percentage change

The general form of these calculations is:

((NewValue – BaseValue) / BaseValue) x 100

For example, the Crystal Palace Eagles (The Pride of South London), won 14 games during the 2018-19 Premiership football season. Suppose they win 24 games in 2019-2020. This would be a 71.4% increase in games won. How so?

Baseline value – 14

New value – 24

((24 – 14) / 14) x 100 = 71.4%

Go Eagles!

100% decrease

Suppose that the Eagles win 0 games in 2019 -2020. Of course, this would never happen but let’s just suppose it does for the sake of argument. This would be a 100% decrease (or, in other words, an increase of negative 100 percent):

((0 – 14) / 14) x 100 = -100%

Decreases of more than 100%

Suppose I have £1,000 in my bank account at the beginning ot the 2019-2020 season. I quit my job, planning to live off of income from my FutureLearn course but no such money materializes. So I survive the year on a diet of Palace Ale which costs me a total of £800 while losing a further £700 betting on The Pride of South London. I tap into the credit allowance of my bank account, leaving a balance of -£500 by the end of the season. My bank balance has suffered a 150% decrease:

((-500 – 1000) / 1000) x 100 = -150%

A factor-of-seven increase

The 2019-20 Eagles exceed all expectations, winning the Premiership and pulling my bank account up to £7,000 despite my increased intake of Palace Ale. This is a 600% increase:

((7000 – 1000) / 1000) x 100 = 600%