SOLUTION: Please help! Kelley has a total of $6 in dimes and quarters. If she has a total of 30 coins, how many quarters does she have? And I have to use it in substitution form an

Algebra ->  Customizable Word Problem Solvers  -> Coins -> SOLUTION: Please help! Kelley has a total of $6 in dimes and quarters. If she has a total of 30 coins, how many quarters does she have? And I have to use it in substitution form an      Log On

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Question 699423: Please help!
Kelley has a total of $6 in dimes and quarters. If she has a total of 30 coins, how many quarters does she have? And I have to use it in substitution form and elimination form.

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +d+ = number of dimes she has
Let +q+ = number of quarters she has
given:
(1) +d+%2B+q+=+30+
(2) +10d+%2B+25q+=+600+ ( in cents )
----------------------
Using substitution,
(1) +q+=+30+-+d+
(2) +10d+%2B+25%2A%28+30+-+d+%29+=+600+
(2) +10d+%2B+750+-+25d+=+600+
(2) +-15d+=+-150+
(2) +d+=+10+
and
(1) +d+%2B+q+=+30+
(1) +10+%2B+q+=+30+
(1) +q+=+20+
She has 10 dimes and 20 quarters
------------------------------
You can do it by elimination, too
Multiply both sides of (1) by +10+
and subtract (1) from (2)
(2) +10d+%2B+25q+=+600+
(1) +-10d+-+10q+=+-300+
+15q+=+300+
+q+=+20+
+d+=+10+
OK