Math 127 - Calculus I - Fall 98 Quiz 8

Suppose that the price p (in dollars) and the weekly sales x (in thousands of units) of a certain commodity satisfy the demand equation

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  1. (6 points) The rate tex2html_wrap_inline95 (in units per week) at which sales are changing satisfy the equation:

    (a) tex2html_wrap_inline97

    (b) tex2html_wrap_inline99

    (c) tex2html_wrap_inline101

    (d) tex2html_wrap_inline103

    (e) tex2html_wrap_inline105

    (f) tex2html_wrap_inline107

    Answer: (e)

  2. (4 points) The rate at which sales are changing at a time when x=100, p=20, and the price is falling at a rate of $2 per week, is:

    (a) -1 units per week
    (b) -2 units per week
    (c) -3 units per week
    (d) -4 units per week
    (e) 1 units per week
    (f) 2 units per week
    (g) 3 units per week
    (h) 4 units per week

    Answer: (h)
    Plug into the equation in Part 1 (e) the given values of x and p and tex2html_wrap_inline113 to get

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    Note: A partial credit of 2 points was given for answer (d).