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Large percentage problem: check my work please?

  1. Apr 28, 2007 #1
    The universe is thought to be 13.7 Billions years old. If you lived to be 100, what percentage of the total age of the universe would coincide with your lifetime?

    I get .0000007% or seven 10-Millionths of one percent.

    Is this correct?
     
  2. jcsd
  3. Apr 29, 2007 #2

    Gib Z

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    [tex]\frac{100}{1.37\cdot10^{10}} \cdot 100 = \frac{10^4}{1.37\cdot 10^{10}} = \frac{1}{1.37\cdot10^6} = 7.2992700729927\cdot 10^{-8}[/tex]

    So you got close, but theres a bit more accurate.
     
  4. Apr 29, 2007 #3
    I'm a bit confused here.

    1 / 1.37 x 10^6 = 1 / 1,370,000 = 0.00000073 = 7.3 x 10^-7

    7.3 x 10^-7 does not equal 7.2992700729927 x 10^-8

    What am I doing wrong???
     
  5. Apr 29, 2007 #4

    Gib Z

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    Well first when you have 13.7 BILLION years the exponent of the 10 is 9, not 6. 6 Is for million. So its 13.7 x 10^9. 13.7 is 1.37 x 10, so it becomes 1.37x10^10

    I don't see what the problem should be, you have the right answer in the beginning! I just gave it a bit more accurately.
     
  6. Apr 29, 2007 #5
    You did the right steps, just made a typo at the end.

    [tex]\frac{1}{1.37\cdot10^6} = 7.2992700729927\cdot 10^{-7}[/tex]
    not
    [tex]\frac{1}{1.37\cdot10^6} = 7.2992700729927\cdot 10^{-8}[/tex]
     
  7. Apr 30, 2007 #6

    Gib Z

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    Damn it! Yes Moo's right...
     
  8. May 1, 2007 #7

    uart

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    I find this thread really ironic. Holocene got the most correct answer, though apparently by accident of inexperience with his calculator and scientific notation etc.

    Gib Z and Moo, you should know it's bad form to give an answers to 15+ significant digits when the data on which the calculations are based is dubious at even two or three significant digits.
     
    Last edited: May 1, 2007
  9. May 2, 2007 #8

    Gib Z

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    14 hehe..Lets settle with [itex]7.3 \cdot 10^{-7}[/itex] :)
     
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