Question

You put 500 pieces of paper in a copy machine. When you check back 6 days later, there are only 320 pieces left. How many pieces of paper are being used each day?

Answer 1

The mean usage over 6 days is 30 per day

Explanation:

Realistically you do not know. One day may use more than another. For example: they may all have been used on day 5 and none on all the other days.

The mean (average) use is all you can determine.

`color(blue)("Determine total count of used pieces of paper")`

`cancel(5)^4 cancel(0)^10 0`
`ul(3color(white)(..)2color(white)(..)0)" "larr" subtract"`
`1color(white)(..)8color(white)(..)0 " "larr" total used"`

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
`color(blue)("Determine the mean use per day")`

Using ratio in fraction format

`" "("Paper count")/("day count")->180/6`

This is for 6 days but we need the count for 1 day

With ratio what you do to the bottom you also do to the top for multiply or divide. This maintains the correct proportions.

`" "("Paper count")/("day count")->(180-:6)/(6-:6) = 30/1`

So the `ul("mean")` usage over 6 days is 30 for each day