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What costs had Mel incurred when his service just began?

The total cost of Mel's cellular phone was $390 after 9 months. What costs had Mel incurred when his service just began?

3 Answers by Expert Tutors

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Jason S. | My goal is the success of my students. Knowledge-Patience-HonestyMy goal is the success of my students. K...
4.9 4.9 (115 lesson ratings) (115)
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I hope I understand the question...
 
390/9 = 43 3/9.
 
43 * 9 months = $387
 
$390 - $387 = $3.
 
 
However, the monthly rate could be $20/month for 9 months = $180
 
390 - 180 = $210
 
 
Most likely more information is needed, just as Pam suggested.
Jamie G. | Spanish Tutor with Master's Degree/Basic Tech HelpSpanish Tutor with Master's Degree/Basic...
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Does the problem tell you how much the monthly charge was? Look for that. It may be in the instructions or in a previous question. With the information you gave us, it is only possible to determine how much the cell phone service cost over the course of 9 months, just as in the equation that Jason did, but you need to have a second variable in order to determine how much Mel started with. Otherwise, you would just say that Mel started with $0, but that is probably not what the question is looking for.  
 
If that is the missing information, here is how you work out that problem: 
 
Let's say that the monthly charge is $30 (I am making up this number.  You can plug in the right number when you get it.)
 
Then you take 30 and multiply it by 9 months (30 x 9 = 270)
Then take the total amount that Mel paid (here you told us that it is $390) and subtract from that amount the total amount for 9 months worth of service, which we just calculated to be $270. (So, 390-270 = 120).  If we use the 30 for our "x" variable, then Mel started off with $120 in costs when his service just began. 
 
 
Pamela E. | Math Tutor for Middle School, High School, and College LevelsMath Tutor for Middle School, High Schoo...
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Are you sure you have listed all the information from the problem? Is there any other information, either in words or in a table or graph?  Looks like more information is needed.