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onegirl

A person scores f(x) = 90/1 + 4e^-0.4t points on a test after t hours of studying. What does the person score without studying at all? Compute f’(0) and estimate how many points 1 hours of studying will add to the score.

  • 11 months ago
  • 11 months ago

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  1. onegirl
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    This is what I did but my teacher said it was wrong she said ( Find f' and f'(0).) F(x) = 90/ 1 + 4e^-0.4t F(0) = 90/ 1 + 4e^-0.4(0) = 18 F(1) = 90/1 + 4e^-0.4(1) = 24.45 So comparing the scote at f(1) and f(0) where at f(1) studying for 1 hour and f(0) studying none. F(1) - f(0)/24.45 – 18 = 6.45 points

    • 11 months ago
  2. EulersEquation
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    Should this have parenteses or not? Is this F(x) = 90/ (1 + 4e^-0.4t )?

    • 11 months ago
  3. onegirl
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    yes prenthesis

    • 11 months ago
  4. onegirl
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    like this \[\frac{ 9 }{ 1 + 4e ^{-0.4t}}\]

    • 11 months ago
  5. EulersEquation
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    Your teacher specifically said to differentiate?

    • 11 months ago
  6. onegirl
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    yes

    • 11 months ago
  7. onegirl
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    she said to Find f' and f'(0)

    • 11 months ago
  8. onegirl
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    @EulersEquation so do you know how?

    • 11 months ago
  9. onegirl
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    @Numb3r1 can u help?

    • 11 months ago
  10. EulersEquation
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    Yes. I need to review this. First glance is to use the quotient rule. Do you know how to use the quotient rule? Someone else may want to take a look. I am in the middle of helping someone else. When I finish I'll get on it.

    • 11 months ago
  11. onegirl
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    ok

    • 11 months ago
  12. EulersEquation
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    Ha! I am terrible at arithmetic. On first run I get a negative number for f'(0). You cannot make a negative score on a test! Unless the teacher doesn't like you. I am rusty on this. I'll work on it some more. In the meantime, bump the problem and hopefully someone else will tackle this.

    • 11 months ago
  13. onegirl
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    okay

    • 11 months ago
  14. onegirl
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    @waterineyes

    • 11 months ago
  15. waterineyes
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    Just want to take derivative of that??

    • 11 months ago
  16. onegirl
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    yes Find f' and f'(0)

    • 11 months ago
  17. waterineyes
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    It will come out to be negative..

    • 11 months ago
  18. onegirl
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    what will come out? so what i did above is wrong or?

    • 11 months ago
  19. waterineyes
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    Wait, let we do it first..

    • 11 months ago
  20. waterineyes
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    \[\frac{ 90 }{ 1 + 4e ^{-0.4t}} = \frac{ -(90)(-1.6 \cdot e^{-0.4t}) }{ (1 + 4e ^{-0.4t})^2}\]

    • 11 months ago
  21. waterineyes
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    It will become positive now.. :)

    • 11 months ago
  22. onegirl
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    okay

    • 11 months ago
  23. EulersEquation
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    Yeah. I don't see why it has to be differentiated -- not according to the question.

    • 11 months ago
  24. waterineyes
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    Am I right in this?

    • 11 months ago
  25. EulersEquation
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    Ah! I forgot to square the denominator!

    • 11 months ago
  26. EulersEquation
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    That looks good.

    • 11 months ago
  27. onegirl
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    okay thanks!

    • 11 months ago
  28. waterineyes
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    So you can now find f'(0) by putting 0 as value of t..

    • 11 months ago
  29. onegirl
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    okay

    • 11 months ago
  30. waterineyes
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    @onegirl can you go for that?

    • 11 months ago
  31. onegirl
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    just plug in 0 and solve right?

    • 11 months ago
  32. waterineyes
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    Yep, just simple calculations with calculator..

    • 11 months ago
  33. onegirl
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    okay yes i can

    • 11 months ago
  34. waterineyes
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    Good.. Keep it up..

    • 11 months ago
  35. onegirl
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    i got 0 after i solved

    • 11 months ago
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