SOLUTION: A jar contains 40 coins consisting of dimes and quarters and having a total value of $4.90. How many of each kind of coin are there? I know that somehow I use .1d+.25q=$4.90 but

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Question 225980: A jar contains 40 coins consisting of dimes and quarters and having a total value of $4.90. How many of each kind of coin are there?
I know that somehow I use .1d+.25q=$4.90 but I don't know how to add the 40 in there. Help please!
Found 2 solutions by scott8148, edjones:
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
two unknowns means two equations

the one with the 40 is ___ "40 coins consisting of dimes and quarters" ___ d + q = 40 ___ d = 40 - q

substituting ___ .1(40-q) + .25q = 4.90

distributing ___ 4 -.1q + .25q = 4.90

subtracting 4 ___ .15q = .90

dividing by .15 ___ q = 6

substituting ___ d + 6 = 40 ___ d = 34

Answer by edjones(8007) About Me  (Show Source):
You can put this solution on YOUR website!
Let d=number of dimes, q=number of quarters
d+q=40
q=40-d
.1d+.25q=4.9 good work.
.1d+.25(40-d)=4.9
.1d+10-.25d=4.9
-.15d=-5.1
d=34
q=6
.
Ed