Answer:
8.4 dollars
Step-by-step explanation:
The error is in the resolution of the proportion. In fact, the initial proportion is correct:
[tex]\frac{5}{3.5}=\frac{12}{x}[/tex]
where x is the total cost. However, the following step of the resolution is wrong. In fact, the correct resolution is the following:
- Multiplying by x on both sides:
[tex]\frac{5x}{3.5}=12[/tex]
- Multiplying by 3.5 no both sides:
[tex]5 x = 12 \cdot 3.5 \\5x = 42[/tex]
And now we can find x:
[tex]x=\frac{42}{5}=8.4[/tex]
So, the total cost is 8.4 dollars.
