SOLUTION: If you buy seven hamburgers and three sodas at a local fast food restaurant, you receive one dollar in change from a $20 bill. If you buy ate hamburgers and two sodas, you receive

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: If you buy seven hamburgers and three sodas at a local fast food restaurant, you receive one dollar in change from a $20 bill. If you buy ate hamburgers and two sodas, you receive       Log On


   



Question 1105045: If you buy seven hamburgers and three sodas at a local fast food restaurant, you receive one dollar in change from a $20 bill. If you buy ate hamburgers and two sodas, you receive $.50 in change from a $20 bill. How much change will you receive from a five dollar bill if you buy one hamburger and one soda
Found 2 solutions by josmiceli, greenestamps:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = the cost of 1 hamburger
Let +b+ = the cost of 1 soda
-------------------------------------
(1) +7a+%2B+3b+=+19+
(2) +8a+%2B+2b+=+19.5+
-------------------------
(1) +7a+%2B+3b+=+19+
(2) +80a+%2B+20b+=+195+
(2) +16a+%2B+4b+=+39+
-------------------------
Multiply both sides of (1) by +4+
Multiply both sides of (2) by +3+
Then subtract (1) from (2)
------------------------------------
(2) +48a+%2B+12b+=+117+
(1) +-28a+-+12b+=+-76+
--------------------------
+20a+=+41+
+a+=+41%2F20+
and
(1) +7%2A%2841%2F20%29+%2B+3b+=+19+
(1) +287+%2B+60b+=+380+
(1) +60b+=+93+
(1) +b+=+93%2F60+
----------------------------
1 hamburger and 1 soda =
+a+%2B+b+=+41%2F20+%2B+93%2F60+
+123%2F60+%2B+41%2F60+=+164%2F60+%0D%0A%7B%7B%7B+164%2F60+=+2+%2B+44%2F60+
+2+%2B+44%2F60+=+2+%2B+11%2F15+
Change from $5 is +2+%2B+4%2F15+
+4%2F15+=+.27+
$2.27 is the change from a $5 bill
check the math!

Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


The other tutor's answer is not right; perhaps you can see where she made her mistake....

7a%2B3b+=+19 you get $1 change from a $20 bill when buying 7 burgers and 3 sodas
8a%2B2b+=+19.5 you get $0.50 change from a $20 bill when buying 8 burgers and 2 sodas

Use elimination: multiply the first equation by 2 and the second by 3 and subtract to eliminate y:
14a%2B6b+=+38
24a%2B6b+=+58.5
10a+=+20.5
a+=+2.05 each burger costs $2.05

Substitute in either original equation to solve for y:
7%282.05%29%2B3b+=+19
14.35=3b+=+19
3b+=+4.65
b+=+1.55 each soda costs $1.55

One burger and one soda costs $3.60; you get $1.40 change from a $5 bill.