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Math Help - Exponential Functions - Check if this is right?

  1. #1
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    Exponential Functions - Check if this is right?

    In 1980 a town's population was 100,000. In 2007 it was 220,000. Estimate what the population will be in 2020 if its growth is exponential.

    y=ka^x
    220,000=100,000a^27
    2.2=a^27
    a = 1.0296

    y=100,000(1.0296)^40
    y=321,174.72

    The population would be roughly 321,174.

    Thats what I got for my answer, but the in the book its saying that y=100,000(1.026)^t is the equation that you would use and that 279,000 would be the population in 2020. Did I do something wrong with the years or is the answer in the back wrong?
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  2. #2
    Senior Member apcalculus's Avatar
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    Quote Originally Posted by peekay View Post
    In 1980 a town's population was 100,000. In 2007 it was 220,000. Estimate what the population will be in 2020 if its growth is exponential.

    y=ka^x
    220,000=100,000a^27
    2.2=a^27
    a = 1.0296

    y=100,000(1.0296)^40
    y=321,174.72

    The population would be roughly 321,174.

    Thats what I got for my answer, but the in the book its saying that y=100,000(1.026)^t is the equation that you would use and that 279,000 would be the population in 2020. Did I do something wrong with the years or is the answer in the back wrong?
    Your work looks fine. I checked with a graphing device as well.
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  3. #3
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    Thank you, appreciate your time.
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