Mrs. Taft keeps inventory of the copy paper in the school copier room. Nine weeks ago, there were 150 reams of copy paper in the room. Now, there are 85 reams left. Which of the following two expressions are equivalent to the average weekly change in the number of reams of copy paper in the copier room over this time period? Choices: -9/65, 9/-65, 65/-9, -65/9 (the negative for this one applies to both numbers.) and -65/-9

where is the figure

the solution of the equation is 2.23 ⇒ answer b

step-by-step explanation:

* lets revise the meaning of exponential function

- the form of the exponential function is y = ab^x, where a ≠ 0, b > 0 ,  

  b ≠ 1, and x is any real number

- it has a constant base b

- it has a variable exponent x

- to solve an exponential equation, take the log or ln of both sides,  

  and solve for the variable

* lets solve the problem

∵

- the base is 7 and the exponent is x

- insert ㏑ in both sides

∴

- use the rule

∴ x ㏑(7) = ㏑(77)

- to find x divide both sides by ㏑(7)

∴

* the solution of the equation is 2.23 to the nearest 2 decimal places

the five is the numerator