Associative law multiplication

You obtain a 20% discount in a warehouse, but you must pay a 15% sales tax. Which would you prefer to have calculated first: discount or tax? Explain. (result write as: 1 = first discount, 2 = first tax, 3 = no matter what first)

Correct answer:

x =  3

Step-by-step explanation:

$$\begin{gathered} p=1000 \\ {a}_1=p\cdot (1-20/100)\cdot (1+15/100)=1000\cdot (1-20/100)\cdot (1+15/100)=920 \\ {a}_2=p\cdot (1+15/100)\cdot (1-20/100)=1000\cdot (1+15/100)\cdot (1-20/100)=920 \\ {a}_1=a_2 \\ x=3 \end{gathered}$$

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