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Question

The number of pieces of mail delivered by the United States Post Office (x years after 1980) can be approximated by m = -0.141x2 + 5.2126x + 52.109, where m is in billions.

Use the equation m=−0.141x2+5.2126x+52.109m=−0.141x 2 +5.2126x+52.109, to determine how many pieces of mail were delivered by the United States Postal Service in 1980, 2000, and 2017. How would you describe the trend in mail delivered? To what do you attribute this? According to this model, when does the pieces of mail delivered reach 20 billion?

Answer 1

x is years after 1980, so in the year 1980, x = 0 (no years since 1980). For year 2000, x = 20, and for 2017, x = 37

 

When x = 0, the function m = -0.141x² +5.2126x + 52.109 resolves to m = 52.109 (since x = 0)

 

Plug x = 20 and x = 37 into the equation to solve for m for the other 2 years.

 

To find when 20 billion is reached, set your equation equal to 20

20 = -0.141x² + 5.2126x + 52.109

and solve for x