Question

a fancy watch was marked up 45% from an original cost of $221.92. last friday, mason bought the watch and paid an additional 9% in sales tax. what was his total cost? $

Explanation:

Step1: Calculate the marked - up price

The original cost is $C_0 = 221.92$. The watch is marked up by 45%, so the marked - up price $C_1$ is the original price plus 45% of the original price. Mathematically, $C_1=C_0\times(1 + 0.45)$.
Substitute $C_0 = 221.92$ into the formula: $C_1=221.92\times1.45 = 221.92\times\frac{145}{100}=221.92\times1.45 = 321.784$.

Step2: Calculate the total cost with sales tax

Now, we need to add a 9% sales tax to the marked - up price. The total cost $C$ is the marked - up price plus 9% of the marked - up price. Mathematically, $C = C_1\times(1 + 0.09)$.
Substitute $C_1 = 321.784$ into the formula: $C=321.784\times1.09=321.784\times\frac{109}{100}=321.784\times1.09 = 350.74456$.

Answer:

$\$350.74$ (rounded to the nearest cent) or $\$350.74456$ (exact value)