Results 1 to 6 of 6

Math Help - [SOLVED] SAT math page 737 #16

  1. #1
    Member
    Joined
    Sep 2008
    Posts
    222

    [SOLVED] SAT math page 737 #16

    If y=\frac{5x^3}{z} what happens to the value of y when both x and z are doubled?

    a) y is not changed
    b) y is halved
    c) y is doubled
    d) y is tripled
    e) y is multiplied by 4

    when both the denominator and numerator are both doubled doesn't it both cancel out and therefore y remains the same?

    Thanks in advance
    Follow Math Help Forum on Facebook and Google+

  2. #2
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by fabxx View Post
    If y=\frac{5x^3}{z} what happens to the value of y when both x and z are doubled?

    a) y is not changed
    b) y is halved
    c) y is doubled
    d) y is tripled
    e) y is multiplied by 4

    when both the denominator and numerator are both doubled doesn't it both cancel out and therefore y remains the same?

    Thanks in advance
    replace x and z with 2x and 2z respectively. what happens to the y-value?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Sep 2008
    Posts
    222
    Quote Originally Posted by Jhevon View Post
    replace x and z with 2x and 2z respectively. what happens to the y-value?
    I got \frac{10x^3}{2z}
    which is the same as \frac{5x^3}{z} isn't it? But how come the correct answer is e) y is multiplied by 4?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by fabxx View Post
    I got \frac{10x^3}{2z}
    which is the same as \frac{5x^3}{z} isn't it? But how come the correct answer is e) y is multiplied by 4?
    that is because \frac {10x^3}{2z} is not what you're supposed to get. i said replace x with 2x and z with 2z. what you did was multiply by 2/2, which is 1, of course you got the same thing back
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    Sep 2008
    Posts
    222
    grr. I still don't get it. Doesn't the question say to double BOTH x and z?
    Follow Math Help Forum on Facebook and Google+

  6. #6
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by fabxx View Post
    grr. I still don't get it. Doesn't the question say to double BOTH x and z?
    yes. that means you change x to 2x and z to 2z as i have been saying

    thus x^3 \to (2x)^3 = 8x^3 and z \to 2z

    when it is all said and done, we have y_{\text{new}} = \frac {5 (8)x^3}{2z} = 4 \cdot \frac {5x^3}z = 4y

    thus y is multiplied by 4
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. [SOLVED] SAT math page 738 #19
    Posted in the Algebra Forum
    Replies: 3
    Last Post: September 29th 2008, 01:42 AM
  2. [SOLVED] SAT math page 718 #8
    Posted in the Algebra Forum
    Replies: 2
    Last Post: September 28th 2008, 12:47 PM
  3. [SOLVED] SAT math page 657 #17
    Posted in the Algebra Forum
    Replies: 5
    Last Post: September 28th 2008, 08:09 AM
  4. [SOLVED] SAT math page 682 #12
    Posted in the Algebra Forum
    Replies: 2
    Last Post: September 28th 2008, 07:04 AM
  5. [SOLVED] SAT math page 657 #18
    Posted in the Math Topics Forum
    Replies: 2
    Last Post: September 28th 2008, 05:28 AM

Search Tags


/mathhelpforum @mathhelpforum