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Numbers divisible by 3

  1. May 22, 2008 #1
    1. The problem statement, all variables and given/known data
    How many 3 digit numbers are divisibIe by 5?


    2. Relevant equations



    3. The attempt at a solution
    I get the answer as 136. could Someone please work it out and check my answer?
     
  2. jcsd
  3. May 22, 2008 #2
    Attempt to a solution?
     
  4. May 22, 2008 #3
    I don't get 136. How did you come up with that answer?
     
  5. May 22, 2008 #4

    Defennder

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    Homework Helper

    I don't get 136 either. How did you get that?
     
  6. May 22, 2008 #5

    Dick

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    Science Advisor
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    There are 'roughly' 20 numbers in every 100 that are divisible by 5. There are 'roughly' 900 three digit numbers. So there are 'roughly' 180 three digit numbers divisible by 5. That's enough off from 136 to make me agree with Defennder and Tedjin. You must be wrong.
     
  7. May 23, 2008 #6
    5, 10, 15, 20, 25, 30

    Its all the numbers that end in 5 or zero, and then ignore the last one (1000) because it had the temerity to posses 4 digits.

    As you start building the sequence, you see the rule easy enough.
     
  8. May 19, 2009 #7
    an=nth term of an AP (Arithmetic progression)
    a=1st term
    d=common difference

    Since the 1st 3 digit no. divisible by 5 is 100
    a=100
    the last 3 digit no. divisible by 5 is 995
    an=995
    common difference (d)=5
    n=no. of 3 digit nos. divisible by 5

    an=a+(n-1)d
    995=100+(n-1)5
    995-100=(n-1)5
    895=(n-1)5
    895/5=n-1
    179=n-1
    179+1=n
    n=180

    Therefore,
    exactly (not roughly) 180 3 digit numbers are divisibe by 5

    Absolutely correct Dick!!!

    @Amith2006
    How did you get 136?!
    :confused:
     
    Last edited: May 19, 2009
  9. May 19, 2009 #8

    Borek

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    Staff: Mentor

    Year that passed since the thread was started was enough to count these numbers using fingers.
     
  10. May 19, 2009 #9
    Aha that made me laugh, insane bump
     
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