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FOR MATHMATE

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Media services charges $40 for a phone and 20/mth for its economy plan. It says to find a model that determines the total cost, C(t), of operationg a media Services phone for t months. I think the answer should be in this equation - y = mx+b. Not sure.



Algebra/Equations,functions - MathMate, Friday, November 26, 2010 at 11:34am
So far so good.

What values would you assign to m and b to complete the operation model?



Algebra/Equations,functions - AMY, Friday, November 26, 2010 at 12:47pm
y = 40x+20?



Algebra/Equations,functions - MathMate, Friday, November 26, 2010 at 1:33pm
Correct!



Algebra/Equations,functions - MathMate, Friday, November 26, 2010 at 1:35pm
Watch out, it's $20/month and the phone (one time only) is $40.
so the equation should be:....




Algebra/Equations,functions - AMY, Friday, November 26, 2010 at 5:19pm
not sure but will take a stab at it. y = 20x +40?



Algebra/Equations,functions - AMY, Friday, November 26, 2010 at 6:44pm
Nope that was wrong on my part. I believe the final answer is C(t) = 20t+40



Algebra/Equations,functions - AMY, Friday, November 26, 2010 at 7:55pm
I also need to find the total cost. This is what I have.

C = 20(0) +40. (0,40).
C (5) = 20 (5) + 40.
C (5) = 100 +40 = 140 (5, 140)
So the total cost is 130. IS THIS RIGHT? Thank you!

  • FOR MATHMATE -

    Thank you for the follow-up. Sorry that I didn't check your responses.

    Yes, in a function, we normally assume that
    C(x)=ax+b
    is equivalent to
    C(t)=at+b
    because t is a "dummy" variable.

    However in your case, t has been stated as the variable, so it is more correct to define function as:
    C(t)=20t+40

    Hope you understood fully why $20 per month is associated with the variable t.

  • FOR MATHMATE -

    Yes. DId you see the total cost?? Was I right with the answer to that one? I think I was right.

  • FOR MATHMATE -

    No, I didn't.

    But if total cost for t months,
    C(t) = 20t + 40, then
    For 0 month:
    C(0) = 20(0)+40 = 40
    for 4 months:
    C(4) = 20(4)+40 = 120
    for 5 months:
    C(5) = 20(5)+40 = 140

    I do not understand how you get 130 (for 5 months)!

    The question has not stipulated for how many months the total cost should be calculated.

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