Results 1 to 3 of 3

Math Help - Formula Manipulation

  1. #1
    Newbie
    Joined
    Oct 2006
    From
    Oslo
    Posts
    2

    Question Formula Manipulation

    Hello!!!!!!!!!!!


    Can anyone help me understand a question:-
    After months of constant practice, Tom manages to improve his time for the 1500m race by 10%. What is the pecentage change in his speed.


    I am not sure about its answer but is it 10%.



    Thank You,
    Mathematician.
    Last edited by Mathematician; October 30th 2006 at 01:14 AM. Reason: I wanted to edit it topic
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member Glaysher's Avatar
    Joined
    Aug 2006
    From
    Newton-le-Willows
    Posts
    224
    Quote Originally Posted by Mathematician View Post
    Hello!!!!!!!!!!!


    Can anyone help me understand a question:-
    After months of constant practice, Tom manages to improve his time for the 1500m race by 10%. What is the pecentage change in his speed.


    I am not sure about its answer but is it 10%.



    Thank You,
    Mathematician.
    Speed = \frac{Distance}{Time}

    s = \frac{d}{t}

    Time is improved by 10% means time reduced by 10% from 100% to 90% which is represented as a decimal by 0.9. So new speed s':

    s' = \frac{d}{0.9t}= \frac{1}{0.9} \frac{d}{t} = 1 \frac{1}{9} s

    So speed has improved from 100% to 111.11...%

    Speed increased by 11 \frac{1}{9}%
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,749
    Thanks
    650
    Hello, Mathematician!

    Glaysher is absolutely correct!
    If you're desperate, insert some numbers and baby-talk through it.


    Tom manages to improve his time for the 1500m race by 10%.
    What is the pecentage change in his speed?

    Suppose Tom took 300 seconds to run 1500 meters.

    . . His speed was: \frac{1500}{300} \:=\:5 m/sec.


    I assume that a "10% improvement" means he takes only 90% of the time now.

    . . So he takes only: 90\% \times 300 \:=\:270 seconds.

    His new speed is: \frac{1500}{270} \;=\;\frac{50}{9} \;=\;5\frac{5}{9} m/sec.


    His speed has increased by: 5\frac{5}{9} - 5 \:=\;\frac{5}{9} m/sec.

    How does this compare with his original speed?

    We have: \frac{\frac{5}{9}}{5} \;= \;\frac{1}{9} \;= \;11\frac{1}{9}\% . . . see?

    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Manipulation of Formula
    Posted in the Algebra Forum
    Replies: 4
    Last Post: October 10th 2011, 11:30 AM
  2. Set manipulation
    Posted in the Discrete Math Forum
    Replies: 6
    Last Post: January 25th 2011, 11:10 PM
  3. Stirling's formula manipulation
    Posted in the Advanced Statistics Forum
    Replies: 5
    Last Post: April 17th 2009, 06:32 AM
  4. help with formula manipulation
    Posted in the Math Topics Forum
    Replies: 1
    Last Post: March 3rd 2009, 02:52 PM
  5. Formula Manipulation
    Posted in the Algebra Forum
    Replies: 1
    Last Post: October 29th 2006, 02:42 AM

Search Tags


/mathhelpforum @mathhelpforum