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Math Help - Need help for Express monthly electricity cost

  1. #1
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    Need help for Express monthly electricity cost

    Electricity company charges customers a base rate of $10 a month, plus 6 cents per kWh for the first 1200 kWh and 7 cents per kWh for all usage over 1200 kWh. Express the monthly cost amount of electricity used.

    My understanding is as below, but not sure if it is correct. Please help!

    Let C as monthly cost, x as electricity usage.


    C(x)=↗ 10+0.06x if x<=1200
    ........↘ 10+0.06x+0.07(x-1200) if x>1200
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  2. #2
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    Quote Originally Posted by Fanlai View Post
    Electricity company charges customers a base rate of $10 a month, plus 6 cents per kWh for the first 1200 kWh and 7 cents per kWh for all usage over 1200 kWh. Express the monthly cost amount of electricity used.

    My understanding is as below, but not sure if it is correct. Please help!

    Let C as monthly cost, x as electricity usage.


    C(x)=↗ 10+0.06x if x<=1200
    ........↘ 10+0.06x+0.07(x-1200) if x>1200
    C(x) = 10 + 0.06x ; x < 1200

    C(x) = 82 + 0.07(x-1200) ; x > 1200
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  3. #3
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    Thanks a lot!
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  4. #4
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    Notice that the only difference is that you have "0.06x" still in the second formula. skeeter replaced that with 0.06 times the entire first 1200 kw hours: .06*12000= $72 which he then added to the base $10 to get $80.
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  5. #5
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    Quote Originally Posted by HallsofIvy View Post
    Notice that the only difference is that you have "0.06x" still in the second formula. skeeter replaced that with 0.06 times the entire first 1200 kw hours: .06*12000= $72 which he then added to the base $10 to get $80.
    Thanks again!
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