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Math Help - basic but needs brains

  1. #1
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    Exclamation basic but needs brains

    please help(as i said, it needs brains )

    1. a worker suffers a 20 percent cut in wages. he regains his original pay buy obtaining a rise of?

    (its not 20...!)

    2. m men can do a job in d days, then the number of days in which m+r men would do the same?

    3. a boy walks from his home to school at 6kmph . walks back at 2 kmph. avg. speed=?
    Last edited by adhyeta; May 1st 2009 at 01:05 AM.
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  2. #2
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    Quote Originally Posted by adhyeta View Post
    please help(as i said, it needs brains )

    1. a worker suffers a 20 percent cut in wages. he regains his original pay buy obtaining a rise of?

    (its not 20...!)
    After the cut he earns 80% of his original income. To rise these 80% to a 100% again he has to add 20%. The percentage is p=\dfrac{20}{80} \cdot 100\% = 25\%

    ...

    3. a boy walks from his home to school at 6kmph . walks back at 2 kmph. avg. speed=?
    Let s denote the distance from home to school. Then the first elapsed time is:

    t_1 = \dfrac s{6\ \frac{km}{h}} and

    t_2 = \dfrac s{2\ \frac{km}{h}}

    The boy walks the distance twice. Then the average speed is:

    v=\dfrac{2s}{t_1+t_2}=\dfrac{2s}{\dfrac s{6\ \frac{km}{h}} + \dfrac s{2\ \frac{km}{h}}} = \dfrac{2s}{\dfrac23  s \ \frac{km}{h}} = 3 \ \frac{km}{h}
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  3. #3
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    thnx. just one more.........
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  4. #4
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    Well? We are waiting impatiently!
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  5. #5
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    Quote Originally Posted by HallsofIvy View Post
    Well? We are waiting impatiently!
    Probably adhyeta is refering to the question #2.

    But I can't answer this question because I don't know what these variables m, r mean ...
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  6. #6
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    Quote Originally Posted by earboth View Post
    After the cut he earns 80% of his original income. To rise these 80% to a 100% again he has to add 20%. The percentage is p=\dfrac{20}{80} \cdot 100\% = 25\%

    ...



    Let s denote the distance from home to school. Then the first elapsed time is:

    t_1 = \dfrac s{6\ \frac{km}{h}} and

    t_2 = \dfrac s{2\ \frac{km}{h}}

    The boy walks the distance twice. Then the average speed is:

    v=\dfrac{2s}{t_1+t_2}=\dfrac{2s}{\dfrac s{6\ \frac{km}{h}} + \dfrac s{2\ \frac{km}{h}}} = \dfrac{2s}{\dfrac23 s \ \frac{km}{h}} = 3 \ \frac{km}{h}
    I'd do question 1 differently.

    Let p_{o} represent his original salary and p_n represent the new.

    From our information, he has received a 20% pay cut, so he is receiving 80% of what he was originally getting.

    p_n = 80\%\textrm{ of }p_o

     = \frac{80}{100}\times p_o

     = \frac{4}{5}p_o.


    Therefore to get back to the original salary

    p_o = \frac{5}{4} p_n

     = \frac{125}{100} \times p_n

     = 125\%\textrm{ of }p_n.


    So he would need a 25% pay increase to get back to his original salary.
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    Quote Originally Posted by earboth View Post
    Probably adhyeta is refering to the question #2.

    But I can't answer this question because I don't know what these variables m, r mean ...

    a typo.
    the questions said-if m men can do a job in d days, then the days reqd for m+r men=?
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  8. #8
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    Quote Originally Posted by adhyeta View Post
    a typo.
    the questions said-if m men can do a job in d days, then the days reqd for m+r men=?
    \begin{array}{lcr}m\ men&\rightarrow\ need \ \rightarrow& \ d\ days \\ 1\ man&\rightarrow\ needs \ \rightarrow& \ m \cdot d\ days \\ m+r\ men&\rightarrow\ need \ \rightarrow &\ \dfrac{m\cdot d}{m+r}\ days \end{array}
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  9. #9
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    lol. thnx earboth. i was doing m men-d days, then 1 man-d/m days.

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