Basic HTML Version
© 2014 Pacific Crest
183
Step
Explanation
2.
Inventory the
information
Make three lists:
1. All information
given
in the problem description
2. What information you feel is
missing
3. What you need to
figure out
Information given:
In 1982 there were fewer than 50,000 mobile phones
In 2000 there were 110 million mobile phones
In 2008 there were 270 million mobile phones
Three quarters of the United States population used mobile phones in 2008
Information missing:
Total population of the United States
Does the increase also work if many people have multiple cell phones (for business
and home, for example)?
What about mobile phones that are thrown away? Are they subtracted or does this
trend just count or consider phones purchased?
What to figure out:
Annual rate of change in quantity of phone ownership
3.
Eliminate
irrelevant
information
Carefully examine the information to see which items can be eliminated
because they are not pertinent to solving the problem.
In 1982 there were fewer than 50,000 mobile phones
In 2000 there were 110 million mobile phones
In 2008 there were 270 million mobile phones
Three quarters of the United States population used mobile phones in 2008
4.
Identify variables,
constants and
assumptions
Identify and define all variables, constants, and assumptions that are
required.
Variables and Constants
y
= the number of years after 2000
n
= the number of phones in millions after
y
years
r
= rate of increase in the number of phones per year
b =
the beginning number of phones in millions (110)
Assumptions
The increase in number of phones from 2000 to 2008 is linear; the period from
2000 to 2008 is likely to be a better predictor of the change from 2008 to 2020.
4.3 Interpreting a Word Problem