An online music club charges $5.75 for the first music download and $2 for each additional download per month. Write a rule for describing the total monthly fees f as a function of additional downloads d. What are the fees for 15 music download ls in a month?

Question

anonymous · Answer

We are given that the online music club charges $5.75 for the first download. So if you download one song, you pay $5.75

We are also given that for every additional download over the first one, the charge is $2.

So the cost for two downloads is:
$5.75 + $2 = $7.75

The cost for three downloads is:
$5.75 + $2 + $2 = $9.75

The cost for four downloads is:
$5.75 + $2 + $2 + $2 = $11.75

So we start to see a pattern here. Also we should note that when we add the same number over and over again, that's multiplication. 

So $2 + $2 is the same as 2 times $2 or $4 total.

anonymous · Answer

We should also see that the number of $2 charges is one less then the number of downloads.

When we have two downloads, there is one $2 charge. 
 
When we have three downloads, there are two $2 charges. 

When we have four downloads, there are three $2 charges. 

So to answer the second part of the question, how much do you pay for 15 downloads.

We subtract one from 15. Which tells us the how many $2 charges there are. 

So 15-1=14  So there are fourteen $2 charges.  Fourteen times $2 equals $28.

Putting it all together, we have the $5.75 charge for the first download plus the $28 charge for the other fourteen downloads. 

So $5.75 + $28 = $33.75 is how much you pay for 15 downloads.

anonymous · Answer

The general equation will be the $5.75 charge for the first download, plus the number of downloads minus one times $2, equals how much you pay.

So we have this as the general equation: 

Let d= the number of downloads
      f= How much you pay.

$5.75 + (d-1)$2= f