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JayDS

  • 3 years ago

14) Juliana has saved her pocket money to buy up to 3 fashion magazines. If there are 5 different magazines to choose from, the number of ways she can buy 1, 2 or 3 magazines is: A) 90 B) 80 C) 25 D) 70 E) 85

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  1. cwrw238
    • 3 years ago
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    if she buys 1 its 5 ways 2 - 5C2 = its 5*4/2 = 10 3 its 5c3 = 5*4*3 / 3*2 = 10 that a total of 25

  2. mukushla
    • 3 years ago
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    number of ways she can buy 1 is C(1,5) number of ways she can buy 2 is C(2,5) number of ways she can buy 3 is C(3,5) C(1,5)+C(2,5)+C(3,5)=25

  3. JayDS
    • 3 years ago
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    the answer is 85....

  4. JayDS
    • 3 years ago
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    which is E.

  5. mukushla
    • 3 years ago
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    let's think again

  6. cwrw238
    • 3 years ago
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    ok - if it depends on the order in which she buys the magazines it is 85 - this wasn't mentioned in the question in this case its 5 + 5P2 + 5P3 = 5 + 20 + 60 = 85 - permutations not combinatons

  7. JayDS
    • 3 years ago
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    this question is under permutations so there should be just a simple way to multiply them but I figured out how it is 85 using nPr, 5P1+5P2+5P3=85 ways.

  8. JayDS
    • 3 years ago
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    ur also using the nPr way, how would u do it using just permutations?

  9. cwrw238
    • 3 years ago
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    nPr means number of permutations of r in n and = n! / r!

  10. JayDS
    • 3 years ago
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    hmm, so it's basically the same?

  11. cwrw238
    • 3 years ago
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    yea - oh ill check on that formula - not sure if its right is it correct?

  12. JayDS
    • 3 years ago
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    i think it's nPr=n!/(n-r)!

  13. cwrw238
    • 3 years ago
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    yup - you r right - my memory failed me there and nCr - n! / r! * (n-r)! right?

  14. cwrw238
    • 3 years ago
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    a quick way of calculating say 5C2 is 5*4 --- 2*1 i.e. number of digits in top and bottom are the same

  15. sunsetlove
    • 3 years ago
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    E.

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