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Exponent Question

  1. Sep 9, 2015 #1
    • Member warned about posting with no effort
    1. The problem statement, all variables and given/known data
    Without using a calculator and without evaluating expressions, determine which is greater. 20^100 or 400^40

    2. Relevant equations
    None, however some exponent laws and possibly mental math are applicable.

    3. The attempt at a solution
    I don't know how to reach an answer without some type of evaluation; which goes against the question.
     
  2. jcsd
  3. Sep 9, 2015 #2

    berkeman

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    You should at least put forth some guesses. Hint -- what can you say about how many zeros will be in each answer?
     
  4. Sep 9, 2015 #3

    Bystander

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    Write 400 in terms of 20.
     
  5. Sep 9, 2015 #4
    I don't know if i am right, but would there be 3 0's in 20^100 and around 4 0's in 400^40?
     
  6. Sep 9, 2015 #5
    What do you mean?
     
  7. Sep 9, 2015 #6

    berkeman

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    No. Please review how exponents work.

    10^2 = 10*10 = 100

    10^3 = 10*10*10 = 1000

    ...and so on... :smile:
     
  8. Sep 9, 2015 #7

    Bystander

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    Can you relate "400" to "20" or "20" to "400?" Are there some simple operations you can perform on either number to get the other?
     
  9. Sep 9, 2015 #8
    well 20 x 20 = 400 or 400/20 = 20
     
  10. Sep 9, 2015 #9

    Bystander

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    Give you any ideas?
     
  11. Sep 9, 2015 #10
    Does that mean that since 20^2 = 400 the 400^40 has to be greater than 20^100. Since 400^2 alone is approximately greater than 20^2.
     
  12. Sep 9, 2015 #11

    Ray Vickson

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    No, it does not mean that; it is not even true.
     
  13. Sep 9, 2015 #12

    Bystander

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    You're playing with the right ideas, but do what Berkeman has recommended regarding laws of exponents; N(k x j) = (Nk)j .
     
  14. Sep 9, 2015 #13
    • Poster has been warned to stop asking for the answer and PM berkeman some work so the thread can be reopened
    then what do you propose the answer is and how would you get to it?
     
  15. Sep 9, 2015 #14
    P
    Please expand. Also how would you reach the answer logically?
     
  16. Sep 9, 2015 #15

    Bystander

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    I'll nudge you in the direction you need to go, but you have to do the work.
    Take what you did earlier,
    pick some values for N, j, k and put them into the general statement I gave you for one of the laws of exponents.
     
  17. Sep 9, 2015 #16
    So would 400^40 be greater because
    So that means that 20^100 is actually greater because 20^ 20x20 is bigger than 400^ 20x2.
     
  18. Sep 9, 2015 #17

    Bystander

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    Quick tutorial on a couple PF features: the Green bar above the reply box will allow you to insert subscripts, x32n2, or superscripts (exponents), x2 or 20100.
    Try redoing what you just did and use this feature --- it might help you visualize just what is "base," (the 20 or the 400) and what is exponent (superscript).
     
  19. Sep 9, 2015 #18

    Ray Vickson

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    PF Rules forbid me from telling you the answer. We can give hints only. You have been given plenty of helpful hints already.
     
  20. Sep 9, 2015 #19

    Mark44

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    I don't believe that you are prohibited from doing every calculation - I think that you don't want you to directly calculate 20400 and 40040. I'm reasonably sure that you are permitted to do some calculations.
     
  21. Sep 9, 2015 #20

    berkeman

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    Thread closed temporarily to discuss the rules with the OP...
     
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