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Prepaid Cellphone Plans

  1. Oct 12, 2011 #1
    How many minutes do you get for $100 if the cellphone plan charges .20 a minute?

    I think it's 500 minutes but I'm not sure...I just kinda guessed randomly in my head. But Im not exactly sure how I came up with it lol.
  2. jcsd
  3. Oct 12, 2011 #2


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    Yes, that's correct. It follows from dividing the two numbers so that the units cancel:

    [tex]\frac{100~\mbox{dollars}}{ 0.2~\frac{\mbox{dollars}}{\mbox{minute}}} = \frac{1000}{2} \frac{\mbox{dollars}~\cdot~\mbox{minute}}{\mbox{dollars}} = 500~\mbox{minutes}.[/tex]

    Of course, that's the theoretical maximum you get. Unless the company does to the second counting, "a minute" is anywhere between 0 seconds and 60 seconds, so the actual total could be less - e.g., make 500 one second phone calls and you might be out $100!
  4. Oct 12, 2011 #3
    Thank you for all of that information! I really appreciate your help.
  5. Oct 12, 2011 #4


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    Most people can think their way through the steps to do this calculation in their head.

    THINK: 20 cents for 1 minute, this upscales to 1 dollar for 5 minutes. You might simply think, "one fifth of a dollar for 1 minute, five times that is 1 dollar for 5 minutes." The ratio is the same.
    Next understand that 100 dollars is 100 times larger than for 1 dollar. Just multiply the "5 minutes" the corresponding factor of 5.
  6. Oct 13, 2011 #5
    How much does each text message cost if I get 250 text messages a month for $5?

    is that 0.02 cents each or something?
  7. Oct 13, 2011 #6


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    In other wording, you ask, "how many dollars for one text message?".
    Simple ratio, and convenient numbers. 5.00 Dollars for 250 messages. You can divide by 5 as simple mental computation. What is that? Your turn!
  8. Oct 13, 2011 #7
    I dunno I already guessed 0.02 cents each.
  9. Oct 13, 2011 #8
    You're pretty good at guessing. :D
  10. Oct 13, 2011 #9


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    Do not guess. Follow the described processes. You should be able to perform the processes in your head. If you cannot do these in your head, then use pencil and paper calculations to find the results.
  11. Oct 13, 2011 #10
    You said to divide 250 by 5 and that comes out to 50. I think you're supposed to divide 5 by 250 though which comes out to 0.02 cents. Why are you asking me for the answer when Im asking you? lol I already said my answer was 0.02 from the beginning but I wanted confirmation that I was right so I know for sure.
  12. Oct 13, 2011 #11
    It comes out to 0.02 dollars, not 0.02 cents.
  13. Oct 13, 2011 #12
    In post #5 Im asking a completely separate question from my original post. Nothing about my first post should be factored into my question in post #5.

    Can you imagine 1 text message costing $2 each haha.
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