phone service and inequality

by wc
(gresham)

For his phone service, Ryan pays a monthly fee of $13.00, and he pays an additional $0.05 per minute of use. The least he has been charged in a month is $72.45.

What are the possible numbers of minutes he has used his phone in a month?

Use m for the number of minutes, and solve your inequality for m.

Solution


Let m be the number of minutes used.


Monthly cost = fixed cost + variable cost


fixed cost = 13


Variable cost = 0.05 × m


Monthly cost = 13 + 0.05m



It says in the problem that the least he has been charged in a month is $72.45.



This means that the monthly cost is at least 72.45.



In other words, the monthly cost is 72.45 or bigger.



This can be expressed as 13 + 0.05m ≥ 72.45



Just solve the inequality.



13 + 0.05m ≥ 72.45



13 - 13 + 0.05m ≥ 72.45 - 13



0 + 0.05m ≥ 72.45 - 13



0.05m ≥ 59.45


Divide both sides by 0.05



0.05m/ 0.05 ≥ 59.45/0.05


m ≥ 1189


Ryan used at least 1189 minutes

Click here to post comments

Join in and write your own page! It's easy to do. How? Simply click here to return to Basic math word problem.

Recent Articles

  1. Graphs of Quantitative Data

    May 18, 21 06:54 AM

    Graphs of quantitative data, also called grouped data, can be displayed using a histogram or a polygon. Learn how to make histograms using raw data

    Read More