SOLUTION: A coin bank contains only nickels, dimes, and quarters. The value of the 31 coins in the bank is $2.80.There are twice as many nickels as dimes. Find the number of each type of coi

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Question 542082: A coin bank contains only nickels, dimes, and quarters. The value of the 31 coins in the bank is $2.80.There are twice as many nickels as dimes. Find the number of each type of coin in the bank.
So far I have done: Dimes=x
Nickels=2x
Quarters=(31-x)
Dimes= 10 times x
Nickels= 5 times 2x
Quarters= 25 (31-x)
5(2x)+10x+25(31-x)=280
10x+10x+775-25x=280<-----doesn't look right.
I believe I am messing up on the quarters section.
Answer by jpg7n16(66) About Me  (Show Source):
You can put this solution on YOUR website!
"So far I have done: Dimes=x" this part is right, though I like to use D for dimes
"Nickels=2x" Again, right.
"Quarters=(31-x)" This is wrong. What you are saying with this equation is that Quarters=31-Dimes. But what about the nickels? should be:
Q=31-d-n=31-d-2d=31-3d or in your case
Q=31-3x
.
"Dimes= 10 times x" Correct
"Nickels= 5 times 2x" Correct
"Quarters= 25 (31-x)" Use above formula.
Q=25%2A%2831-3x%29
And solving:
10x%2B5%2A2x%2B25%2A%2831-3x%29=280
10x%2B10x%2B775-75x=280
-55x=-495
x=9
And I believe you've got it from here! Hope this helps