What is 50% of 100? 50, right? What is 50% of 50? 25, right? Now apply the same logic if you decrease 100 by 50% and then increase the resulting number by 50%, what do you get?
Certainly, if he had indicated earlier that the equation he was referring to includes both units and percentages. However, Yang only discussed percentages.
Comments
$90 + 10% = $99
True
100% - 10% = 90%
90% + 10% = 100%
True