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andjie

  • 2 years ago

Can someone explain this for me step by step? Abby rows 10 km upstream and 10 km back in a total time of 3 hr. The speed of the river is 5 km/h. Find Abby’s speed in still water. @mark_o.

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  1. andjie
    • 2 years ago
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    You found me lol

  2. mark_o.
    • 2 years ago
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    yeah im here now lol :D |dw:1354646559750:dw|

  3. mark_o.
    • 2 years ago
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    she row from starting point A to B then from B to A that is time from A to B + time from B to A = 3 hours

  4. andjie
    • 2 years ago
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    ok

  5. mark_o.
    • 2 years ago
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    time Tab + T ba = 3 (1) but distance d=velocity x time,. therefore t=d/v dAB dBA ------ + ------- =3 but distances dBA=dAB=10 km v v 10 10 ------- + ------ =3 v v but note that velocity of river is v=5 km/hr for upstream v= v+5 10 10 for down stream v= v-5, therefore ------- +------ = 3 v+5 v-5 you can algebra now ion finding v=?

  6. mark_o.
    • 2 years ago
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    i mean you can do the algebra now from this point ... :D

  7. andjie
    • 2 years ago
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    ummmm I am stuck

  8. andjie
    • 2 years ago
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    I am sorry lol

  9. mark_o.
    • 2 years ago
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    10/(v+5) + 10 /(v-5) =3 10(v-5) + 10(v+5) ------------------ =3 (v+5)(V-5)

  10. mark_o.
    • 2 years ago
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    do multiplication and addition to simplify the numerator and the denominator..:D

  11. andjie
    • 2 years ago
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    give me a sec

  12. andjie
    • 2 years ago
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    wow i suck cause I am lost

  13. andjie
    • 2 years ago
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    |dw:1354590455411:dw|

  14. andjie
    • 2 years ago
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    |dw:1354590757893:dw|

  15. andjie
    • 2 years ago
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    the v is throwing me off

  16. mark_o.
    • 2 years ago
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    10 10 -------- + ------- = 3 (v+5) (v-5) ? ------------------- =3 (v+5) (v-5)

  17. andjie
    • 2 years ago
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    20

  18. andjie
    • 2 years ago
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    |dw:1354591224584:dw|

  19. mark_o.
    • 2 years ago
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    for the further left, that is (v+5)(v-5) -----------= ? then mult by 10 (v+5)

  20. mark_o.
    • 2 years ago
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    then on the mid of it (v+5)(v-5) -----------= ? then mult by 10 (v-5)

  21. andjie
    • 2 years ago
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    |dw:1354591397442:dw|

  22. mark_o.
    • 2 years ago
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    10(v-5) + 10(v+5 ------------------- = 3 (v+5)(v-5)

  23. andjie
    • 2 years ago
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    |dw:1354591544810:dw|

  24. andjie
    • 2 years ago
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    ok give me a sec and let me figure this out

  25. mark_o.
    • 2 years ago
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    multiply the numerator then do addition on the denominator multiply them also

  26. andjie
    • 2 years ago
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    |dw:1354591871260:dw|

  27. andjie
    • 2 years ago
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    is that right

  28. mark_o.
    • 2 years ago
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    hhm where did you get 10-5 and 15+5 from? it should stay as 10( v-5)=? and 10(v+5)=?

  29. andjie
    • 2 years ago
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    I SUBTRACTED AND ADDED 10 FROM BOTH (V-5)(V+5)

  30. andjie
    • 2 years ago
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    10-5=5 AND 10+5=15

  31. andjie
    • 2 years ago
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    I just want to understand it

  32. Hero
    • 2 years ago
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    I guess you didn't like my explanation

  33. andjie
    • 2 years ago
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    no i asked you a question and you left

  34. andjie
    • 2 years ago
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    I just hate math and it takes me awhile to get it together

  35. Hero
    • 2 years ago
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    Well, I just answered your question

  36. Hero
    • 2 years ago
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    I left the room to help someone else with their question, but you should not assume that I had left.

  37. mark_o.
    • 2 years ago
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    it should stay as 10( v-5)=? and 10(v+5)=? 10( v-5)= 10v -50 is it ? and 10(v+5)= 10v +50 is it ?

  38. mark_o.
    • 2 years ago
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    ahh you have posted this before..yeah @andjie when we start coaching you dont assume that we had left .. :D

  39. andjie
    • 2 years ago
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    Thank you I am sorry

  40. Hero
    • 2 years ago
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    @mark_o. I am convinced you are doing this the hard way.

  41. mark_o.
    • 2 years ago
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    and for the denominator (v+5)(V-5)=?

  42. mark_o.
    • 2 years ago
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    haha i know..:D im sorry @Hero ...:D

  43. Hero
    • 2 years ago
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    Go check out my solution

  44. mark_o.
    • 2 years ago
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    where is that? lol... :D

  45. Hero
    • 2 years ago
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    I'll do anything to avoid a quadratic equation

  46. Hero
    • 2 years ago
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    Besides, I don't like when you get to a result where you have two solutions but have to discard one of them because it is negative.

  47. mark_o.
    • 2 years ago
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    i think andjie is just doing the refresher thing now.. to recall everything .. that was 7 years ago ? @ andjie?

  48. andjie
    • 2 years ago
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    9 almost ten years ago

  49. Hero
    • 2 years ago
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    http://openstudy.com/study#/updates/50bd6019e4b0de42629fcb42

  50. andjie
    • 2 years ago
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    wait I just had my high school reunion so it was 10 years ago lol

  51. Hero
    • 2 years ago
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    She's probably 28 years old

  52. mark_o.
    • 2 years ago
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    wow, almost 10 years ago? hmmm yeah this is a good refresher to you ... :D

  53. andjie
    • 2 years ago
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    29

  54. Hero
    • 2 years ago
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    I just posted a link to the solution

  55. mark_o.
    • 2 years ago
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    hhhm i cant open it, dont know why @Hero

  56. andjie
    • 2 years ago
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    I understand this better @hero hopefully I can do more like this

  57. Hero
    • 2 years ago
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    d = rt and let r = b ± w b = speed of the boat w = speed of the water current t1 = Upstream time t2 = Downsteam time 10 = 5t 2 = t1 t1 + t2 = 3 2 + t2 = 3 t2 = 3 - 2 t2 = 1 Upstream Formula d = rt1 d = (b - w)t1 Downsteam Formula: d = rt2 d = (b + w)t2 b - w = 5 Upstream 10 = 2(b - w) Downsteam 10 = (b + w) 10 = 2b - 2w 20 = 2b +2w 30 = 4b 30/4 = b 7.5 = b 10 = b + w 10 = 7.5 + w 10 - 7.5 = w 2.5 = w Therefore The speed of the boat was 7.5 km/h

  58. mark_o.
    • 2 years ago
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    ok this is good,, directly for the solutions and answer.... ;D

  59. mark_o.
    • 2 years ago
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    you did really avoid the quadratic equation .. :D

  60. andjie
    • 2 years ago
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    You guys are just too smart for me

  61. Hero
    • 2 years ago
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    I usually find ways to avoid it.

  62. Hero
    • 2 years ago
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    It's a personal goal of mine

  63. andjie
    • 2 years ago
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    lol

  64. mark_o.
    • 2 years ago
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    ok that is very good.... and andjie can copy this one to study and do for a second solution or alternate solution..........:D

  65. andjie
    • 2 years ago
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    Thank you @mark_o. you always look out for me

  66. Hero
    • 2 years ago
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    Well, back to watching Smallville. I'm trying to get to the end of the 10th season and it's taking forever.

  67. andjie
    • 2 years ago
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    Have fun and thank you for your help

  68. mark_o.
    • 2 years ago
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    ok YW,, tc now and have fun solving..........:D

  69. mark_o.
    • 2 years ago
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    thanks for doing the alternative solution, that was a good one :D @Hero...............:D

  70. Hero
    • 2 years ago
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    You're welcome. I have plenty alternative solutions up my sleeve.

  71. Hero
    • 2 years ago
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    If you need an alternative solution, cite me.

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