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anonymous

  • one year ago

I don't know why I am getting the wrong answer, please help! 16. The first term of an arithmetic progression is 6 and the fifth term is 12. The progression has n terms and the sum of all the terms is 90. Find the value of n. I will post a picture of my working out.

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  1. anonymous
    • one year ago
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  2. anonymous
    • one year ago
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    The correct answer is 8

  3. Nnesha
    • one year ago
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    i got 8 !! :D now wait a sec i'll check ur work

  4. Nnesha
    • one year ago
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    http://prntscr.com/8ig2duis it 45/n ??

  5. anonymous
    • one year ago
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    The screenshot didn't work

  6. anonymous
    • one year ago
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    But in the beginning I did get 45/n

  7. Nnesha
    • one year ago
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    okay so at left side is it 45/n it's a 2nd row

  8. Nnesha
    • one year ago
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    how did you get that ?

  9. anonymous
    • one year ago
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    Oooh...I combined 1/2 n and 90. not like terms so I cant do that right?

  10. Nnesha
    • one year ago
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    it's \[\frac{ 3 }{ 2}n = \frac{3n}{2}\] n isn't at the denominator

  11. Nnesha
    • one year ago
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    ye first combine 12-3/2

  12. Nnesha
    • one year ago
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    \[\huge\rm 90=\frac{ n(\color{Red}{12}+\frac{ 3 }{ 2 }n-\color{Red}{\frac{ 3 }{ 2} })}{ 2 }\] like terms

  13. anonymous
    • one year ago
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    Ok. I will try again quickly.

  14. Nnesha
    • one year ago
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    okay :=)

  15. anonymous
    • one year ago
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    I got 7.46, Did I lose some accuracy somewhere or is that what I am meant to get?

  16. Nnesha
    • one year ago
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    yes that's not correct

  17. anonymous
    • one year ago
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    Awwww. Oh well. Ok should i post my working out again?

  18. Nnesha
    • one year ago
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    yes

  19. welshfella
    • one year ago
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    a + 4d - a = 4d = 12 - 6 = 6 so d = 3/2

  20. Nnesha
    • one year ago
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    first multiply both sides by 2 \[\huge\rm 90 · 2=\frac{ n(\color{Red}{12}+\frac{ 3 }{ 2 }n-\color{Red}{\frac{ 3 }{ 2} })}{ 2 }· 2\] combine 12-3/2 and then distribute parentheses by n

  21. anonymous
    • one year ago
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  22. anonymous
    • one year ago
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    the n=9 is from the other equation

  23. anonymous
    • one year ago
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    Oh. I think I forgot that its over 2

  24. Nnesha
    • one year ago
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    no you didn't you distributed the parentheses by (1/2)n

  25. anonymous
    • one year ago
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    Yes?

  26. anonymous
    • one year ago
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    I'm sorry, I don't really understand whaI did wrong?

  27. Nnesha
    • one year ago
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    i know what happened t o12.25 ?? check ur 6th and 7th row

  28. anonymous
    • one year ago
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    I was making a perfect square

  29. Nnesha
    • one year ago
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    w|dw:1442760681511:dw| you should add (b/2)^2 to both sides

  30. Nnesha
    • one year ago
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    it's n^2 ** typo

  31. anonymous
    • one year ago
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    Oh!! I forget to do that a lot >:/ Ok, third time lucky. Trying again.

  32. anonymous
    • one year ago
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    Aaaaand I am finally getting it right!

  33. Nnesha
    • one year ago
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    Yahooo!!

  34. anonymous
    • one year ago
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    Thank you for your patience and for helping me so much! :D

  35. Nnesha
    • one year ago
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    my pleasure &GREAT JOB!! i like how u posted ur work :=) that was super cool!

  36. Nnesha
    • one year ago
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    good luck!!

  37. anonymous
    • one year ago
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    Thanks!

  38. Nnesha
    • one year ago
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    o^_^o

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