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    A quantity has the value P at time t seconds and is decreasing at a rate
    proportional to P .

    Given that when t = 0, P = 400,
    b find the value of a.
    Given also that when t = 30, P = 100,
    c find the value of P when t = 50.



    Hello I had a question to ask : initially I didn't put -k in order to indicate that it is decreasing . But I still ended up with the answer they have given in the mark scheme? how come?
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    (Original post by laurawoods)
    A quantity has the value P at time t seconds and is decreasing at a rate
    proportional to P .

    Given that when t = 0, P = 400,
    b find the value of a.
    Given also that when t = 30, P = 100,
    c find the value of P when t = 50.



    Hello I had a question to ask : initially I didn't put -k in order to indicate that it is decreasing . But I still ended up with the answer they have given in the mark scheme? how come?
    Your k will be negative where their k is positive. The result is the same in the end.
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    (Original post by Mr M)
    Your k will be negative where their k is positive. The result is the same in the end.
    So is not compulsary to to put the - in front of the k when in the question you have got a decreasing rate?
    this was the question (question no 7 on here)
    http://www.london-oratory.org/maths/...s/E4Qint_L.pdf
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    (Original post by laurawoods)
    So is not compulsary to to put the - in front of the k when in the question you have got a decreasing rate?
    this was the question (question no 7 on here)
    http://www.london-oratory.org/maths/...s/E4Qint_L.pdf
    No it doesn't matter at all.
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    (Original post by laurawoods)
    So is not compulsary to to put the - in front of the k when in the question you have got a decreasing rate?
    this was the question (question no 7 on here)
    http://www.london-oratory.org/maths/...s/E4Qint_L.pdf
    think of it like this. Well more specifically. By putting K, you should be saying ( or thinking) this k represents a negative number. Whereas -k , you should be thinking k is a positive number ( constant) , so -k is a negative number and representing the decrease.

    So what you did was implicity assume k was negative .
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    (Original post by Mr M)
    No it doesn't matter at all.
    hmmm . i never thought that way! thanks!
 
 
 
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