Solve $\text{Price: }+20\%\text{ then }-10\%$

Step-by-step solution

1. Step 1 · Multiply percentage factors
   $$P_{\text{final}}=P(1.20)(0.90)=1.08P$$

   The decrease applies to the increased price, not to the original price.

2. Step 2 · Measure against the original
   $$(1.08-1)\cdot 100\%=8\%$$

   For a 100-unit example, the price rises to 120 then falls to 108. Subtracting percentages would wrongly give 10%.