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anonymous

  • 5 years ago

solve by elimination 0.3x-0.2y=4 0.4x+0.3y=-1

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  1. amistre64
    • 5 years ago
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    muliply by 10 to get rid of the decimals... that will make it look less intimidating

  2. amistre64
    • 5 years ago
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    3x-2y = 40 4x +3y = -10

  3. Yuki
    • 5 years ago
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    if you multiply 40 on the first eqn and 30 on the second, you can see which ones can be eliminated

  4. Yuki
    • 5 years ago
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    your idea is to make the coefficients of either x or y to be equal

  5. Yuki
    • 5 years ago
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    for most elimination problems, that will work

  6. amistre64
    • 5 years ago
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    to eliminate the x variables; *4 the top and *3 the bottom...then subtract

  7. amistre64
    • 5 years ago
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    12x -8y = 160 12x +9y = -30

  8. amistre64
    • 5 years ago
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    we could combine these steps by mulitply one equation by a negative instead... 12x -8y = 160 -12x -9y = 30 --------------- -17y = 190 y = -190/17

  9. anonymous
    • 5 years ago
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    you lost me

  10. amistre64
    • 5 years ago
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    where?

  11. anonymous
    • 5 years ago
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    12x-8y=160 12x-9y=-30 how did you get those

  12. amistre64
    • 5 years ago
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    by subtraction...... 12x -8y = 160 12x -8y = 160 -(12x +9y = -30) means -12x -9y = 30 ---------------- ----------------

  13. amistre64
    • 5 years ago
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    tell me: does this equal out? 5 5 -(-4) +4 ---- ---- ???

  14. anonymous
    • 5 years ago
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    yes

  15. amistre64
    • 5 years ago
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    thats all i did..... just with more numbers involved

  16. anonymous
    • 5 years ago
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    how did you get the 12x -8y = 160 & -(12x +9y = -30)

  17. amistre64
    • 5 years ago
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    elimination means 'get rid of something'...right? the only way to get rid of something; to eliminate it; is to get it to zero... otherwise there is something still there right?

  18. anonymous
    • 5 years ago
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    right

  19. amistre64
    • 5 years ago
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    you are given 2 equations and are asked to eliminate something.... that would either be the xs or the ys right? I choose the xs cause they were in front.

  20. anonymous
    • 5 years ago
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    ok

  21. amistre64
    • 5 years ago
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    do you recall that in an equation..whatever you do to one side has to be done to the other to keep it equal?

  22. anonymous
    • 5 years ago
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    yes

  23. amistre64
    • 5 years ago
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    5+3 = 8 when we multiply this by 4 is it still equal? 4(5+3 = 8)..... 20 + 12 = 32 ???

  24. anonymous
    • 5 years ago
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    right

  25. amistre64
    • 5 years ago
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    do the variables make a difference to it? 4(5x + 3y = 4)......20x +12y = 16...still equal??

  26. amistre64
    • 5 years ago
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    we are not changing the 'value'...just the form, its shape, the way it looks..... the value remains the same. right?

  27. anonymous
    • 5 years ago
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    right

  28. amistre64
    • 5 years ago
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    so lets use this to our advantage.. we want some part of your equation to cancel each other out... what wer ethe equations again?

  29. amistre64
    • 5 years ago
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    0.3x-0.2y=4 0.4x+0.3y=-1 we can multiply both equation by 10 to get rid of the decimal and make it easier to look at right? we change the shape; but not the value

  30. anonymous
    • 5 years ago
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    k

  31. amistre64
    • 5 years ago
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    3x - 2y = 40 4x +3y = -10 we good here?

  32. anonymous
    • 5 years ago
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    yes

  33. amistre64
    • 5 years ago
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    we have no terms that are the same...so we have to modify some more..... to get rid of one of them.....or rather a set of them.

  34. amistre64
    • 5 years ago
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    if we pick 'x'...what value do 4x and 3x have in common?

  35. anonymous
    • 5 years ago
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    x?

  36. amistre64
    • 5 years ago
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    x is not a 'value' :) 4x and 3x..... do they have 12x in common? 8x? 29x?

  37. amistre64
    • 5 years ago
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    x is a valued pick; but that makes things messier lol

  38. amistre64
    • 5 years ago
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    valid pick is what its spose to say...

  39. amistre64
    • 5 years ago
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    4x(3) = 12x 3x(4) = 12x.....right?

  40. anonymous
    • 5 years ago
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    right

  41. amistre64
    • 5 years ago
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    so the top can be *4; and the bottom *3 4(3x - 2y = 40) 12x -8x =160 3(4x +3y = -10) 12x +9y = -30 havent changed anything but the way they look correct?

  42. anonymous
    • 5 years ago
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    correct

  43. amistre64
    • 5 years ago
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    but if we add these together...nothing is eliminated is it?... what do we have to do to get an elimination now?

  44. anonymous
    • 5 years ago
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    wouldnt x be eliminated

  45. amistre64
    • 5 years ago
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    how? 12x + 12x = 24x..... that aint zero..

  46. anonymous
    • 5 years ago
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    your right i was thinking bout -12x +12x continue plz

  47. amistre64
    • 5 years ago
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    thats right... we need to change the way one of them looks again to get a -12x... 12x -8x =160 12x -8x =160 -1(12x +9y = -30) -12x -9y = 30..now were good to go

  48. amistre64
    • 5 years ago
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    can we eliminate now?

  49. anonymous
    • 5 years ago
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    yes

  50. amistre64
    • 5 years ago
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    we get: -17y = 190..... solve for y y = -190/17. right?

  51. anonymous
    • 5 years ago
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    yes

  52. amistre64
    • 5 years ago
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    since we have a solid value for y...use it to find x

  53. anonymous
    • 5 years ago
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    wait how does 190 become -190 and -17 becomes 17

  54. amistre64
    • 5 years ago
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    the negative doesnt care what its attached to..... any (+)(-) combonation results in a (-)...right? does 190/-17 equal something different than -190/17?

  55. anonymous
    • 5 years ago
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    i guess not

  56. amistre64
    • 5 years ago
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    the proper ettiquiette is to put the sign to the top...

  57. amistre64
    • 5 years ago
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    but in some cases its good to know that you can move it around

  58. amistre64
    • 5 years ago
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    what wouldve hapened aif we combined steps?

  59. amistre64
    • 5 years ago
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    .4(.3x -.2y = 4) .12x -.08y = 1.6 -.3(.4x+.3y =-1) -.12x -.09y = .3 ----------------- -.17y = 1.9 y = -1.9/.17 = -190/17

  60. anonymous
    • 5 years ago
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    right

  61. amistre64
    • 5 years ago
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    0.4x+0.3y=-1 .4x + .3(-190/17) = -1....solve for x

  62. anonymous
    • 5 years ago
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    -5.7

  63. anonymous
    • 5 years ago
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    or is it -133/17

  64. amistre64
    • 5 years ago
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    4x = -10 + 570/17 4x = (-170 + 570)/17 4x = 400/17 x = 400/4.17 = 100/17

  65. amistre64
    • 5 years ago
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    4.17 is a lazy way of writing 4*17

  66. anonymous
    • 5 years ago
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    how did yiu get 570/17

  67. amistre64
    • 5 years ago
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    i used 3(-190/17) instead of .3(-190/17) 3(-190) = -570 ------ ------ 17 17 4x - 570/17 = -10 4x = -10 + (570/17)...

  68. anonymous
    • 5 years ago
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    oh ok i was doing it by .3

  69. amistre64
    • 5 years ago
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    :) .3 was fine, but you would have had to change the decimal eventually

  70. amistre64
    • 5 years ago
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    1/.17 cahnges to 100/17

  71. anonymous
    • 5 years ago
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    -10*17=-170

  72. amistre64
    • 5 years ago
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    .4x + .3(-190/17) = -1 .4x - 57/17 = -1 .4x = -1 + (57/17) .4x = (-17+57)/17 .4x = 40/17 x = 40/(.4*17) x = 400/(4*17) x = 100/17

  73. anonymous
    • 5 years ago
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    ok i think i got it

  74. amistre64
    • 5 years ago
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    i think i see you trying to get rid of the 17 on the bottom :)

  75. anonymous
    • 5 years ago
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    i just dont know how to do this stuff

  76. anonymous
    • 5 years ago
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    taking midterms this week these questions are for the practice exam

  77. amistre64
    • 5 years ago
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    68x - 570 = -170 68x = -170 + 570 x = 400/68 x = 400/4 100 ------- = ----- 68/4 17

  78. amistre64
    • 5 years ago
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    i got a final grade of 89.06%...and it gave me an 'A' for the course ;)

  79. amistre64
    • 5 years ago
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    i dropped 3 writing assignments and still passed with an 'a' lol

  80. anonymous
    • 5 years ago
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    thats good! right now i have a 77.37%

  81. anonymous
    • 5 years ago
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    how did you get those answers above 68x....

  82. amistre64
    • 5 years ago
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    i times everything by 17 to get rid of the fraction...

  83. amistre64
    • 5 years ago
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    4(17) = 68

  84. anonymous
    • 5 years ago
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    right but 3(17)=51

  85. amistre64
    • 5 years ago
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    3(-190)(17) ---------- = 3(-190) (17)

  86. amistre64
    • 5 years ago
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    17/17 = 1

  87. anonymous
    • 5 years ago
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    x=400/68 i divide that by?

  88. amistre64
    • 5 years ago
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    thats why its called getting rid of a fraction ;)

  89. amistre64
    • 5 years ago
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    400/68 has 4 in common..remember 4(17)? and 4(100) = 400

  90. amistre64
    • 5 years ago
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    divide them both by 4

  91. anonymous
    • 5 years ago
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    ok now that way makes sense to me

  92. amistre64
    • 5 years ago
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    you seem to see numbers and math is a solid concrete building that cant be moved or messes with. but its really more like silly putty...bend it to your will :)

  93. amistre64
    • 5 years ago
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    algebra has 5 rules: and only 5 rules...

  94. anonymous
    • 5 years ago
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    whats that?

  95. amistre64
    • 5 years ago
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    1. numbers can be moved around (commutative) 2. numbers canbe grouped in different ways (associative) 3. every number has an evil twin (inverse). 4. there is one number that changes nothing (identity) 5. distribute numbers thru paranthesis (distributive)

  96. anonymous
    • 5 years ago
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    i will have to make a note of those

  97. amistre64
    • 5 years ago
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    3 and 4 are split in 2 by some people to get an additivie inverse/multiplicative inverse and an additive indentity/multiplicative identity

  98. amistre64
    • 5 years ago
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    tell me; the 1st rule says we can move number around... 4-5 is the same as -5+4 right?

  99. anonymous
    • 5 years ago
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    yes =-1

  100. amistre64
    • 5 years ago
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    -10 + 6 is the same as 6 - 10 right? when you move numbers...pack their luggage, there signs :)

  101. amistre64
    • 5 years ago
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    does grouping matter? 3*(4*5) is the same as (3*4)*5 right?

  102. anonymous
    • 5 years ago
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    same

  103. amistre64
    • 5 years ago
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    3+(5-6) the same as (3+5)-6? but you gotta keep an eye out for this sometimes....

  104. amistre64
    • 5 years ago
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    3-5-6 ^ never split a negative/subtractionwith a parenthesis

  105. amistre64
    • 5 years ago
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    3+(-5-6) is the same as (3-5)-6

  106. amistre64
    • 5 years ago
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    subtraction and division are make believe..... there is only addition and multiplication that is real.

  107. anonymous
    • 5 years ago
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    yes=-8

  108. amistre64
    • 5 years ago
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    3-5 means 3+-5

  109. amistre64
    • 5 years ago
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    5-2 means 5+ -2

  110. amistre64
    • 5 years ago
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    the evil twin rule.... accounts for subtraction and division...

  111. amistre64
    • 5 years ago
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    what is the evil twin of 15? its -15 the evil twin of -3 .... is 3

  112. amistre64
    • 5 years ago
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    the evil twin of 6, when multiplying is 1/6 tho..... thats why some people split the rules

  113. anonymous
    • 5 years ago
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    thought it was -6

  114. amistre64
    • 5 years ago
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    additions evil twin is the opposite of a number; -9 ; 9 multiplications evil twin is the upside down; 8 ; 1/8

  115. amistre64
    • 5 years ago
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    recpirocal is an upside down fraction rigt? the evil multplication twin of 3/4 is 4/3 the evil addition twin of 3/4 is -3/4

  116. amistre64
    • 5 years ago
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    the evil addition twin of 18 is -18 teh evil multiplication twin of 18 is 1/18

  117. amistre64
    • 5 years ago
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    what is the addition identity number? 4 + ? = 4 -9 + ? = -9 17 - ? = 17

  118. amistre64
    • 5 years ago
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    what is the multiplcation identnty number? 6*? = 6 14*? = 14 (-5/8)*(?) = -5/8

  119. amistre64
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    when evil twins meet; they form the identity number: 4+ -4 = 0 12 + -12 = 0 -7 + 7 = 0 4(1/4) = 1 2/5(5/2) = 1 (129/17) (17/129) = 1

  120. amistre64
    • 5 years ago
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    and rule 5; distribution 5(3+6) = 45 5(3) + 5(6) = 45 15 + 30 = 45 45 = 45

  121. amistre64
    • 5 years ago
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    whatever we can distribute together; we can undistribute as well...which is what we cal factoring quadratic equations

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