SOLUTION: Mandy has 11 coins in dimes and quarters. The value of her coins is $2.15. How many dimes does she have?

Question 368931: Mandy has 11 coins in dimes and quarters. The value of her coins is $2.15. How many dimes does she have?
Answer by lkellhomes(6) (Show Source): You can put this solution on YOUR website!
Given that the number of dimes and the number of quarters totals 11, we can set up two equations.
d + q = 11
The value of a dime is .10 and the value of a quarter is .25
so the value of each coin is multiplied by the quantity of each coin.
.10d + .25q = $2.15
We now have two equations and two unknowns. Use substitution to solve
Equation 1: d + q = 11 or q = 11 - d
Equation 2: .10d + .25q = $2.15
Substitute the modified Equation 1 into Equation 2
.10d + .25q = 2.15
.10d + .25(11-d) = 2.15 ----distribute
.10d + 2.75 - .25d = 2.15 ---combine like terms
-.15d + 2.75 = 2.15 ----subtract 2.75 from both sides
-.15d = -.60 ----divide both sides by .15
d = 4
Mandy has 4 dimes
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