Answer:
- A bag of rice is $16.9
- A bag of flour is $5.20
Explanation:
Let R and F stand for the price of a bag of Rice and Flour, respectively.
We can use the information provided to set an equation that will predict the total cost for that restaurant, given the quantities of rice and flour received (Restaurants A and B)
A) 4R + 2F = 78 [4 bags of rice and 2 bags of flour, when multiplied by the prices per bag, R and F, will result in a total cost of $78.
B) 3R + 4F = 71.5 [Now it is 3 bags of rice and 4 of flour, for a total cost of $71.50
We have 2 equations and 2 unknowns. We can use substitution to find the answers. Take one of the equations and reorganize it to isolate one of the variables (R or F). We'll take the equation for A and isolate F
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A) 4R + 2F = 78
2F = 78-4R [subtract 4R from both sides]
F = 39-2R [divide both sides by 2]
We've isolated F, and we can use this definition of F in the second equation:
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B) 3R + 4F = 71.5
3R + 4(39 - 2R) = 71.5 [Use the definition of F derived above. In this manner, we have legally eliminated one of the two variables. (Sneaky, effective, and fun)]
3R + 156 - 8R = 71.5 [Multiply, combine like terms, and simplify]
-5R = -84.5 [Isolate R]
R = $16.9 A bag of rice costs $16.9
Now use the price of rice (R=$16.9) in one of the equations. Since the rearranged equation we used above is already conveniently written for F, we'll use it:
F = 39 - 2R
F = 39 - 2(16.9)
F = 39 - 33.8
F = $5.20 A bag of flour costs $5.20
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CHECK:
Do these two prices satisfy both equations we first formulated?
Restaurant A: 4R + 2F = 78?
4(16.9) + 2(5.20) = 78 YES
Restaurant B: 3R + 4F = 71.5?
3(16.9) + 4(5.20) = 71.5 YES
These are the correct answers.