SOLUTION: I have 30 coins consisting of 5 cent and 20 cent coins. If the total value of these coins is 4.05$, how many 5 cent coins do I have? I tried making a table, didn't work for me.

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Question 1059246: I have 30 coins consisting of 5 cent and 20 cent coins. If the total value of these coins is 4.05$, how many 5 cent coins do I have?
I tried making a table, didn't work for me.

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
I don't use tables, but here's how I do it:
Let +a+ = number of 5 cent coins
Let +b+ = number of 20 cent coins
--------------------------------------
(1) +a+%2B+b+=+30+
(2) +5a+%2B+20b+=+405+ ( in cents )
------------------------
Multiply both sides of (1) by +5+
and subtract (1) from (2)
(2) +5a+%2B+20b+=+405+
(1) +-5a+-+5b+=+-150+
--------------------------
+15b+=+255+
+b+=+17+
and
(1) +a+%2B+b+=+30+
(1) +a+%2B+17+=+30+
(1) +a+=+13+
--------------------
You have 13 5 cent coins
You have 17 20 cent coins
---------------------------
check:
(2) +5a+%2B+20b+=+405+
(2) +5%2A13+%2B+20%2A17+=+405+
(2) +65+%2B+340+=+405+
(2) +405+=+405+
OK