cell phone company Y charges a $10 start up fee plus $0.10 per minute, x. Cell phone company Z charges $0.20 per minute, x, with no start up fee. Which function represents the difference in cost between company Y and company Z?
A.) f(x) = -0.10x-70
B.) f(x) = -0.10x+10
C.) f(x) = 10x-0.10
D.) f(x) = 10x+0.10



Answer :

B.
There is a 10 cent difference in the cost per minute, which is where the -.10x comes from. There is also a 10 dollar difference in the start up fees, which gives you the +10. 

So, if you were to choose Cell phone company Z, you would lose 10 cents per minute, but save gain 10 dollars at the beginning. -10x+10

Function that represents the difference in cost between company Y and company Z is

[tex]f(x)=-0.10x+10[/tex]

Given :

Cell phone company Y charges a $10 start up fee plus $0.10 per minute, x.

Lets frame equation for each company

Company Y

Charge y = cost per minute (x) + initial start up fee

[tex]y=0.10x+10[/tex]

Cell phone company Z charges $0.20 per minute, x, with no start up fee

[tex]y=0.20x+0[/tex]

Now we write the difference in cost

Subtract the cost to find the difference in cost

[tex]f(x)=0.10x+10-0.20x\\f(x)=-0.10x+10[/tex]

Function represents the difference in cost between company Y and company Z is

[tex]f(x)=-0.10x+10[/tex]

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