80%
1) Since the prices on Target dropped from $15 to $12 to find the equivalent percentage of $12 in comparison to $15 we need to write down the following ratio:
[tex]\begin{gathered} 15----100\% \\ 12----x\% \\ \frac{15}{12}=\frac{100}{x} \\ 15x=12\cdot100 \\ \frac{15x}{15}=\frac{1200}{15} \\ x=80\% \end{gathered}[/tex]Note that we cross multiplied that ratio and then on the second step we have divided both sides by 15.
2) Hence, I paid 80% of the original price that day
