REally confused????? Help me plz?

Question

ok i have this math problem and its really confusing i don't understand it all its 2 cell phone companies are promoting cell phone plans. Company A offers a flat fee of $90.00 per month. Company B offers a different plan. It will cost $15 per month of service and $.10 per minute. You will need to compare the two plans to decide which cell phone company is the best for you. i know ur not suppose to do this for me but just need some advise on how to do it.

Answer 1

Plan A    90

Plan B    15 + .10x , where x represents the # of minutes used per month

I suggest you graph the two and find the point of intersection.  Use a graphing calculator if you have one.

Plan B is the better deal until you hit the point of intersection, then Plan A is better.  

Good luck to you !

Answer 2

Here is a way to cheat on almost any problem like this...use the units.  Keep the units right on any calculation and you have a good shot at solving it.

You want to compare dollars/month, right?  That determines which plan is more expensive.  One plan is a flat 90 dollars/month so you don't need to do anything there.  The other is 15 dollars/month + 0.1dollars/minute.  Even if you know nothing about cell phone plans, it makes sense that you have to compare dollars/month to dollars/month so you need to turn that dollars/minute into dollars/month.  You have to cancel out minutes in the denominator so you know you need minutes in the numerator of whatever you are going to multiply by.  You want months in the denominator so minutes/month works.  Multiply minutes/month*dollars/minute and minutes cancel leaving you with dollars/month.  Try this with a few values of minutes/month.

The value you may be most interested in is 75 dollars/month since this is the difference in the dollars/month of the 2 plans.  Again, cancel units. 75 dollars/month=.1dollars/minute*X minutes/month.  I am sure you can make this work

Answer 3

You need to write an equation for Company B to find the cost depending on the number of minutes used that is 15 + .10 x  then setting equal to the 90 flat fee you will find that if you are going to use 750 minutes both plans will cost $90  

Now to compare which is best depends on your usage.  If you are going to use less than 750 minutes the per minute plan is best, but if you are going to use more than 750 minutes the flat fee is better.