# Prepaid Cellphone Plans

1. Oct 12, 2011

How many minutes do you get for $100 if the cellphone plan charges .20 a minute? I think it's 500 minutes but I'm not sure...I just kinda guessed randomly in my head. But Im not exactly sure how I came up with it lol. 2. Oct 12, 2011 ### Mute Yes, that's correct. It follows from dividing the two numbers so that the units cancel: $$\frac{100~\mbox{dollars}}{ 0.2~\frac{\mbox{dollars}}{\mbox{minute}}} = \frac{1000}{2} \frac{\mbox{dollars}~\cdot~\mbox{minute}}{\mbox{dollars}} = 500~\mbox{minutes}.$$ Of course, that's the theoretical maximum you get. Unless the company does to the second counting, "a minute" is anywhere between 0 seconds and 60 seconds, so the actual total could be less - e.g., make 500 one second phone calls and you might be out$100!

3. Oct 12, 2011

### Embison

Thank you for all of that information! I really appreciate your help.

4. Oct 12, 2011

### symbolipoint

Most people can think their way through the steps to do this calculation in their head.

THINK: 20 cents for 1 minute, this upscales to 1 dollar for 5 minutes. You might simply think, "one fifth of a dollar for 1 minute, five times that is 1 dollar for 5 minutes." The ratio is the same.
Next understand that 100 dollars is 100 times larger than for 1 dollar. Just multiply the "5 minutes" the corresponding factor of 5.

5. Oct 13, 2011