SOLUTION: Need help setting up and solving following word problem----Four large cheeseburgers and two chocolate shakes cost a total of $7.90. Two shakes cost $0.15 more than one cheeseburger

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Question 806696: Need help setting up and solving following word problem----Four large cheeseburgers and two chocolate shakes cost a total of $7.90. Two shakes cost $0.15 more than one cheeseburger. What is the cost of a cheesburger? A shake?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = the cost in cents of a cheeseburger
Let +b+ = the cost in cents of a shake
-----------------------------------
(1) +4a+%2B+2b+=+790+
(2) +2b+=+a+%2B+15+
------------------
Always make sure that the number of equations
matches the number of unknowns- it does.
(2) +-a+%2B+2b+=+15+
Subtract (2) from (1)
(1) +4a+%2B+2b+=+790+
(2) +a+-+2b+=+-15+
+5a+=+775+
+a+=+155+
and
(2) +2b+=+a+%2B+15+
(2) +b+=+%281%2F2%29%2Aa+%2B+15%2F2+
(2) +b+=+155%2F2+%2B+15%2F2+
(2) +b+=+170%2F2+
(2) +b+=+85+
--------------
A cheeseburger costs $1.55
A shake costs $.85
check:
(1) +4a+%2B+2b+=+790+
(1) +4%2A155+%2B+2%2A85+=+790+
(1) +620+%2B+170+=+790+
(1) +790+=+790+
OK