SOLUTION: a collection of 70 coins consisting of dimes, quarters, and half-dollars has a value of $17.75. There are three times as many quarters as dimes. find the number of each kind of coi

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Question 149607: a collection of 70 coins consisting of dimes, quarters, and half-dollars has a value of $17.75. There are three times as many quarters as dimes. find the number of each kind of coin.
Answer by Fombitz(32388) About Me  (Show Source):
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D-dimes
Q-quarters
H-half dollars
1.D%2BQ%2BH=70 Total count of coins.
2.0.10D%2B0.25Q%2B0.50H=17.75 Total value of coins.
3.Q=3D Three times dimes equals quarters.
Use eq. 3 to substitute for Q in eq. 1 and 2.
1.D%2BQ%2BH=70
D%2B3D%2BH=70
We'll call that equation 1a.
1a.4D%2BH=70
.
.
.
.
2.0.10D%2B0.25Q%2B0.50H=17.75
First multiply by 100 to get rid of decimals.
10D%2B25Q%2B50H=1775
10D%2B25%283D%29%2B50H=1775
10D%2B75D%2B50H=1775
We'll call that equation 2a.
2a.85D%2B50H=1775
Use eq. 1a to come up with an expression for H as a function of D.
1a.4D%2BH=70
H=70-4D
Now substitute into eq. 2a,
2a.85D%2B50H=1775
85D%2B50%2870-4D%29=1775
85D%2B3500-200D=1775
-115D=-1725
D=15
From eq. 3,
Q=3D
Q=3%2815%29
Q=45
From 1a,
H=70-4D
H=70-4%2A15
H=70-60
H=10
There are 15 dimes, 45 quarters, and 10 half dollars.