[SOLVED] Warren has 40 coins, worth $4.05....

[Conaanaa]

I always have trouble with problem solving!

Warren has 40 coins (all nickels, dimes, and quarters) worth $4.05. He has 7 more nickels than dimes. How many quarters does Warren have?

This is what my chart looks like:

---------|--------------|-------|------------------|
         |    Number    | Value |   Total Value    |
---------|--------------|-------|------------------|
Nickels  |     7+d      |    5  |      5(7+d)      |
Dimes    |      d       |   10  |       10d        |
Quarters | 40 - (7+d+d) |   25  | 25[40 - (7+d+d)] |
---------|--------------|-------|------------------|

But I need help with the equation! I'm not sure if the chart is right either

 

[stapel]

Sum the "total value" expressions", and set equal to the given total value of 405 cents. Then solve for the value of d. Back-solve for the numbers of coins.

Eliz.

 

[Goistein]

5(7+d)+10d+25[40-(7+d+d)]=405
7+d+2d+200-35-5d-5d=81
91=7d
d=13
n=13+7=20
q=40-d-n=40-13-20=7