Math
posted by Mary on .
A collection of 30 coins worth $5.50 consists of nickels, dimes, and quarters. There are twice as many dimes as nickels. How many quarters are there?

Let the number of nickels be N
let the number of dimes be D, so D = 2N
let the number of quarters be Q
but Q would then be 30ND
= 30  N  2N
= 30  3N
now form an equation using the "value" of those coins:
5(N) + 10(2N) + 25(303N) = 550
solve for N, then backsubstitute for the others.
Let me know what you got. 
so i did...
5n+10(2n)+75075n=550
5n+20n75n=200
50n=200
n=4
four nickels
eight dimes
12 quarters
.. that's not right! D: 
4 nickels
8 dimes, and
3048 = 18 quarters, (how did you get 12?)
check: 4(5) + 8(10 + 18(25) = 550 
ohh!
for some reason i multiplied 4 and three to get 12 quarters..
wow silly mistake!
thanks so much for the help!! 
fuch et just guess