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Math Help - Probabilities hw

  1. #1
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    Probabilities hw

    Hi, so I have this math homework due for oct 31. I actually don't need an answer, I only want someone to tell me if my answers are correct or not. thanks!

    Ok, i only did 2 questions so far haha

    is this correct?: 12!=12!x11!x10!x9!x8!x7!x6!x5!x4!x3!x2!x1! = 479 001 600

    and: (14 3) [14 is on top and 3 on the bottom] = 14!/3!(14-3)! = 14!/3!11! = 14x13x12/6 = 364
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  2. #2
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    Re: Probabilities hw

    Quote Originally Posted by xluux View Post
    Hi, so I have this math homework due for oct 31. I actually don't need an answer, I only want someone to tell me if my answers are correct or not. thanks!

    Ok, i only did 2 questions so far haha

    is this correct?: 12!=12!x11!x10!x9!x8!x7!x6!x5!x4!x3!x2!x1! = 479 001 600

    and: (14 3) [14 is on top and 3 on the bottom] = 14!/3!(14-3)! = 14!/3!11! = 14x13x12/6 = 364
    12! = 12 x 11 x 10 x 9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 = 479 001 600, not what you wrote.

    Your second question is correct.
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    Re: Probabilities hw

    thanks! i actually wrote what you just wrote on my paper...my brain is kinda tired
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    Re: Probabilities hw

    Eid?
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    Re: Probabilities hw

    Quote Originally Posted by Prove It View Post
    12! = 12 x 11 x 10 x 9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 = 479 001 600, not what you wrote.

    Your second question is correct.
    Is this correct? A74= 7!/(7-4)! = 7!/3!
    Qo2: Access codes to the school’s network were given to students, teachers and technicians in a local high school: students’ codes are composed of 4 different letters followed by 3 different numbers. Professors’ are formed of 2 letters (different or not) followed by 4 numbers (different or not). Technicians’ are made up of 1 letter and followed by 5 different numbers.

    1. How many different access code this high school can make?
    2. What is the probability that the symbols composing a professors’ code are all different?
    3. We know the letters and numbers composing a student’s code but do not know in which order they are disposed. What is the probability of finding the right combination the first time?


    a) I had a little trouble finding the answers to this question…but here’s what I found:
    Students: L264= 26!/(26-4)!=26!/22!
    N103= 10!/(10-3)!=10!/7!
    LxN= 26!/22! x 10!/7! = (22x10)!/(7x26)! = 220!/182!
    Students have the possibility of 220!/182! Different access codes.

    Teachers: L=(262)= 26!/2!(26-2)!= 26!/2!24!=26x25/2=325
    N= (104)= 10!/4!(10-4)!= 10!/4!6! = 10x9x8x7/24= 210
    LxN= 325x210 = 68250
    Teachers have the possibility of 68250 different access codes.

    Technicians: L= 1/26
    N= A105= 10!/(10-5)! =10!/5! = 3628800/120
    1/26 x 3628800/120 = 15120/13
    Techs have the possibility of 15120/13 different access codes
    So the whole high school can make 220!/182! + 68250 + 15120/13 different access codes…and I’m stuck here because I don’t know how to sum all of this up =/ a little help please?

    b) L262= 26!/(26-2)! = 26!/24!
    N104= 10!/(10-4)! = 10!/6!

    • (26x6)!/(24x10)! = 156!/240!

    The probability that a teacher’s access code is composed of different numbers and letters is 156!/240! [correct?]

    c) I can't find the right formula to find the answer the this one.
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