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回答
There was a $25 discount on every purchase of $75there was a 10% charge on shipping which was added before the discount and 20% sales tax after the discount was added. If john paid total $300, what was the original amount of purchase if no sales tax was added per $75
每购买75$, shipping charge=75*0.1=$7.5; fee after shipping=75$+7.5$=$82.5
fee after discount=82.5-25=57.5. sale tax=57.5*0.2=11.5.
75$(11.5 sale tax), $300 means 4*11.5=46$,
original amount of purchase=300$-46$=254$