Answer: $56.97
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Step-by-step explanation:
"25% off" means the buyer pays 75% of the original cost, ignoring any other taxes, fees, shipping, etc.
75% = 75/100 = 0.75
Multiply this decimal value with the original cost 72 and we get 0.75*72 = 54.
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Now we compute the sales tax
5.5% = 5.5/100 = 0.055
0.055*54 = 2.97 is paid in tax
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Add the sales tax ($2.97) to the discount price ($54) to get 54+2.97 = 56.97
We don't add on shipping because that is free. The sales tax is applied after the discount is done, or else it would imply that the 25% discount didn't fully go through (ie you are paying some portion of what was promised to be saved)
A shortcut is to compute: 72*0.75*1.055 = 56.97 which allows us to basically find the answer in one single step. The 1.055 refers to the 5.5% tax multiplier. A similar trick can be used if you have multiple discounts applied simultaneously.