



 
Hi Matthew, Think about what you would do if you knew the original price and you wanted to calculate the retail price after an 80% markup. Suppose the original price was $\$p.$ To calculate the retail price you would find 80% of $\$p$ and add it to $\$p.$ Thus the retail price would be \[\$p + 0.80 \times \$p = 1.80 \times \$p.\] Thus you have \[1.80 \times \$p = \$99.\] Since $\$99$ is 1.80 times $\$p$ you know that $\$p$ is $\$99$ divided by 1.80. I hope this helps,  


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