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Playing With Percentages

Professor Michael Spagat's video helps you to handle percentages like a pro and to support the Crystal Palace Eagles in the English Premiership

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%

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Survival Statistics: Secrets for Demystifying Numbers

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