Let the number of nickels found be n, the number of dimes be d and the number of quarters be q.
i) "you have twice as many quarters as dimes and 42 coins in all."
means that 2d=q, and n+d+q=42
we can reduce the number of unknowns by substituting q with 2d:
n+d+q=42
n+d+2d=42
n+3d=42
We can write all n, d and q in terms of d as follows:
there are n=42-3d nickels, d dimes and q=2d quarters.
ii) In total there are $6.60 dollars,
1 nickel = 5 cent = $0.05
1 dime = 10 cent = $0.1
1 quarter = 25 cent = $0.25
thus
(42-3d)*0.05 + d*0.1 +2d*0.25= $6.60
2.1 - 0.15d+0.1d+0.5d=6.60
2.1+0.45d=6.6
0.45d=6.6-2.1=4.5
d=4.5/0.45=10
iii)
so, there are 10 dimes, 2d=2*10=20 quarters and 42-3d=42-3*10=12 nickels.
Answer: 10 dimes, 20 quarters, 12 nickels
