SOLUTION: Laura has 20 coins consisting of quarters and dimes. If she has a total of $3.05, how many dimes does she have?

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Question 358419: Laura has 20 coins consisting of quarters and dimes. If she has a total of $3.05, how many dimes does she have?

Found 2 solutions by mananth, robertb:
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
20 coins
dimes & quarters
value 305 cents
let dimes be x
quarters will be 20-x
...
25(20-x)+10x=305
500-25x+10x=305
-15x=-195
/-15
x=13
dimes 13
quarters 7 coins
...
m.ananth@hotmail.ca

Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
q+d = 20.
0.25q + 0.10d = 3.05.
The first equation gives q = 20-d. By direct substitution,
0.25(20-d) + 0.10d = 3.05,
5-0.25d + 0.10d = 3.05,
-0.15d = -1.95,
d = 13, q = 7.