Math CentralQuandaries & Queries


Question from Jay:

When calculating percentage growth, why is (y-x)/x the same as (y/x)-1 ??? (I seem to be stuck on the simple algebra here)...

e.g. 2011, toy was £5, 2012, toy is £10. What is the percentage increase? So, (10-5)/5 = 1 (i.e. 100% increase), AND, (10/5)-1 = 1 (i.e. also 100% increase).

Thanks in advance.

Hi Jay,

Write $1 = \large \frac{x}{x}$ and then

\[\frac{y}{x} - 1 = \frac{y}{x} -\frac{x}{x} = \frac{y - x}{x}\]

I hope this helps,

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