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Math Help - urgent ~~ Zzz

  1. #1
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    urgent ~~ Zzz

    i udn understand question.. help mi wif tis questions
    Attached Thumbnails Attached Thumbnails urgent ~~ Zzz-scan0011.jpg  
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  2. #2
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    Hello, xiaoz!

    Seven men can paint a bridge in 15 days.
    (1) How long woud it take 3 men?

    One man can paint \frac{1}{7} of the bridge in 15 days.
    In one day, one man can paint \frac{1}{105} of the bridge.

    Hence, 3 men can paint 3 \times \frac{1}{105} = \frac{1}{35} of the bridge in one day.


    Therefore, it will take the 3 men 35 days to paint the bridge.



    (2) The bridge was painted in t days.
    Write an expression, in terms of t,
    for the number of men needed to paint the bridge.

    Some information is missing . . .

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  3. #3
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    Greetings Xiaoz:

    If y varies directly with the square of x, then the relation between x and y is: y = kx^2, where k is a constant. Given y = 10 for some value of x, which I shall call xt, it follows that 10 = k(xt)^2. Now, dividing xt by 2 gives k(xt / 2)^2 on the right. And elimination of parentheses leaves k*(xt)^2 / 4. Hence dividing xt by 2 has the effect of dividing k(xt)^2 by 4. (This is only logical, yes? Dividing a squared quantity by 2 is equivalent to inserting factor, 1/2, within the 'squared parentheses'. The action yields 1/4 upon squaring). Anyway, if k(xt)^2 = 10, then it follows that [k(xt)^2] / 4 = 10/4 = 5/2 or 2.5.

    I hope this was instructive.

    Rich B.
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  4. #4
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    (1b1)
    There is an easier method to use rather than Soroban's.

    Work is inversely proportional to rate.
    Thus, if it takes 15 days for 7 men how long for 3 men and x days.
    Since we have a inverse proprtion we know,
    15\times 7=3\times x
    Thus,
    x=35
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