Answer: The number of dimes is:
Dimes = -(Nickels + Pennies) + 24.
Such that Nickels + Pennies < 24, and each quantity refers to the initial number of coins of the given type.
Step-by-step explanation:
Let's call N = number of nickels, D = number of dimes, and P = number of pennies.
The total number of coins is N + D + P
We know that the total value in nickels is:
N*$0.05
The total value in dimes is:
D*$0.10
And the total value on Pennies is:
P*$0.01
Then, the "mean" value of the coins will be equal to the total value of all the coins, divided the total number of coins.
$0.07 = (N*$0.05 + D*$0.10 + P*$0.01)/(N + D + P)
we can mutiply at both sides by the total number of coins, and we have:
$0.07*(N + D + P) = N*$0.05 + D*$0.10 + P*$0.01
Now, if we remove one nickel by five penies, we have:
$0.06 = ((N-1)*$0.05 + D*$0.10 + (P+5)*$0.01)/(N - 1 + D + P + 5)
Again, we multiply in both sides by the total number of coins and:
$0.06*(N - 1 + D + P + 5) = ((N-1)*$0.05 + D*$0.10 + (P+5)*$0.01)
Ok, now we have two equations:
$0.07*(N + D + P) = N*$0.05 + D*$0.10 + P*$0.01
$0.06*(N + D + P + 4) = ((N-1)*$0.05 + D*$0.10 + (P+5)*$0.01)
We can take the second equation and write the right side as:
$0.06*(N + D + P + 4) = ((N-1)*$0.05 + D*$0.10 + (P+5)*$0.01)
= N*$0.05 + D*$0.10 + P*$0.01 - 1*$0.05 + 5*$0.01
= N*$0.05 + D*$0.10 + P*$0.01
Now, the two equations are:
$0.07*(N + D + P) = N*$0.05 + D*$0.10 + P*$0.01
$0.06*(N + D + P + 4) = N*$0.05 + D*$0.10 + P*$0.01
Then we have that:
$0.07*(N + D + P) = $0.06*(N + D + P + 4)
D*($0.07 - $0.06) = ($0.06 - $0.07)*(N + P)) + 4*$0.06
D*$0.01 = -$0.01(N + P) + 4*$0.06
D = (-$0.01(D + P) + 4*$0.06)/$0.01 = -(N + P) + 24
So the number of Dimes is related to the number of pennies and nickels that we have at the begginig.
Such that in both cases the number of dimes is equal:
D = -(N + P) + 24
Notice that N + P can not be larger or equal than 24, so we have the rule:
N + P < 24.
D
