Answer: C = 1.06P
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Explanation:
The sales tax is 6% of the price P
6% of P = 0.06P
Add on the original cost P to get P+0.06P = (1+0.06)P = 1.06P
The 1.06 indicates the final after tax cost is 106% of the original price.
You can think of it like 100% + 6% = 106% = 1.06
So that's how we end up with C = 1.06P
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An example using actual numbers:
Let P = $100 be the initial cost before tax
6% of P = 0.06*P = 0.06*100 = 6 dollars is the tax
100+6 = 106 is the final cost
Note how C = 1.06P = 1.06*100 = 106
