Eric has 130 coins consisting of nickels and quarters. The coins combined value comes to $15.90. Find out how many of each coin Eric has.

Question

phi · Answer

Can you pick two variables for the unknowns?

mathmale · Answer

and also define what those two variables represent?

anonymous · Answer

n would be .05 and .25 would be for q right

phi · Answer

You mean let n be the *number of nickels*  , right ?

mathmale · Answer

0.05 is the value of a nickel, in dollars; .25 the value of a quarter, in dollars.
But what about the COUNTS of how many nickels and how many quarters we have?

phi · Answer

The question asks for the *number* of each coin.  So that should be the variable ... it is what you want to solve for.

phi · Answer

so, to continue:

n is the number of nickels
q is the number of quarters

what does this mean:
Eric has 130 coins consisting of nickels and quarters
?

phi · Answer

The idea is you change the English statement into an equation

Can you take a stab at it?

anonymous · Answer

-.05n + -.05q=6.5 
.05n + .25q=15.90
.25=15.90
q=79.2
does n =-50.5?

phi · Answer

Not so fast.   Think about this:  you have n nickels  and q quarters
what is the sum of n and q ?

phi · Answer

For example,  using numbers (instead of letters)
you have 3 nickels and 4 quarters
how many coins do you have? How do you figure it out?  You would say
3 Plus 4 is how many coins I have

Use that idea, but now use the letters.

mathmale · Answer

And, Veronica, ask yourself:  What would you think if I told you I had -50.5 nickels and 79.2 quarters?  Not trying to be funny; it's important that you ask yourself whether your results are reasonable or not.

anonymous · Answer

n would 50.5 and not -50.5

phi · Answer

I guess you are missing the idea.  
n is the number of nickels.   You will only have whole numbers of nickels. 

If you have 3 nickels and 4 quarters, how many coins do you have ?

anonymous · Answer

15n and$ 4.00for q

phi · Answer

To solve this problem, you have to understand a few ideas.

The first idea is howl to solve this (simple) problem:
If you have 3 nickels and 4 quarters, how many coins do you have ?
can you answer that question ?