ANSWER
EXPLANATION
Sara has 25 coins.
They are made up of quarters and dimes.
Let the number of quarters be q.
Let the number of dimes be d.
Therefore:
q + d = 25____(1)
She has a total of $3.40.
One quarter is worth $0.25
One diime is worth $0.10
Therefore, the number of quarters multiplied by the value of a quarter plus the number of dimes multiplied by the value of a dime is going to be $3.40:
0.25q + 0.10d = 3.40 _____(2)
We now have a system of equations:
q + d = 25____(1)
0.25q + 0.10d = 3.40 _____(2)
From (1):
q = 25 - d
Put this in (2):
0.25(25 - d) + 0.10d = 3.40
=> 6.25 - 0.25d + 0.10d = 3.40
Collect like terms:
6.25 - 3.40 = 0.25d - 0.10d
2.85 = 0.15d
=> d =
