SOLUTION: lauren purchased a box of burgers for 35$ at her usual grocery store. When she got back home she saw a flyer for a different store advertising a price that was 50 cents less per b

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Question 1135052: lauren purchased a box of burgers for 35$ at her usual grocery store. When she got back home she saw a flyer for a different store advertising a price that was 50 cents less per burger. if laura has shopped at the second store she could have bought 8 more burgers for the same price
what was the price of one of the burgers lauren bought?

Found 5 solutions by swincher4391, greenestamps, Alan3354, ikleyn, MathTherapy:
Answer by swincher4391(1107) About Me  (Show Source):
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Let B be the cost of a burger.
Let N be the number of burgers in a box.

N * B = $35
(N+8)*(B-.50) = $35
N = 35/B
(35/B+8)*(B-.50) = 35
(35+8B)/B * (B-.50) = 35
(35+8B)/(B-.5) = 35B
(35+8B) = 35B(B-.5)
(35+8B) = 35B^2 - 17.5B
35B^2 -25.5B - 35 = 0
quadratic formula x+=+%28-%28-25.5%29+%2B-+sqrt%28+%28-25.5%29%5E2-4%2A35%2A35+%29%29%2F%282%2A35%29+
Yields two answers, but only one is positive (since we're talking about money after all).
Hence the answer is $1.43 per burger.


Answer by greenestamps(13198) About Me  (Show Source):
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There are many ways to solve this kind of problem. The following is likely not the easiest -- just what seems to me the "obvious" way to get started.

Let n be the number of burgers and p be the price of each. Then

np+=+35 the cost of the burgers she bought was $35
%28n%2B8%29%28p-1%2F2%29+=+35 the cost of 8 more burgers at a price 50 cents less each would also have been $35

np+=+%28n%2B8%29%28p-1%2F2%29
np+=+np-%281%2F2%29n%2B8p-4
8p+=+%281%2F2%29n%2B4
16p+=+n%2B8
n+=+16p-8

Substitute that back into the first equation:

p%2816p-8%29+=+35
16p%5E2-8p+=+35
16p%5E2-8p-35+=+0
%284p-7%29%284p%2B5%29+=+0
p+=+7%2F4+=+1.75 or p+=+-5%2F4+=+-1.25

A negative price doesn't make any sense, so the price per burger she paid was $1.75.

CHECK: $35 at $1.75 each --> 20 burgers;
28 burgers at $1.25 each = $35

Answer by Alan3354(69443) About Me  (Show Source):
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ooooh, someone tell Fat Donny.

Answer by ikleyn(52775) About Me  (Show Source):
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.
At the first store the price for one burger was  35%2Fn dollars, where "n" was the number of burgers in the box.


At the second store there were (n+8) burgers in their box for the same cost of 35 dollars per box,

so the cost of one single burger was  35%2F%28n%2B8%29  dollars.   


The difference in price for one single burger is 50 cents = 0.5 dollar, which gives you an equation


    35%2Fn - 35%2F%28n%2B8%29 = 0.5   dollars.    (1)


To solve this equation, multiply both sides by 2*n*(n+8). You will get


    70(n+8) - 70n = n*(n+8).


Simplify and then solve this quadratic equation


    70n + 70*8 - 70n = n^2 + 8n

    n^2 + 8n - 560 = 0.


Factor left side


    (n+28)*(n-20) = 0.


Only positive root  n = 20  is meaningful - so it is the solution.


Answer.  There were 20 burgers in the box at the first store at the price  35%2F20 = $1.75 per one burger.


CHECK.  I will check if the equation (1) is satisfied.

        The price for 1 burger at the first store is  35%2F20 = 3500%2F20 cents = 175 cents.

        The price for 1 burger at the second store is  35%2F28 dollars = 3500%2F28 = 125 cents, or exactly 0.5 dollars less.

        So the problem is solved correctly (!)

Solved.

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I like this approach:  it is short and straightforward,  and at every step of building the base equation (1) you follow
exactly to the problem's description.  It prevents you of making errors - as much as possible.

In this site,  there are several lessons,  where you can find similar problems explained ans solved
    - Challenging word problems solved using quadratic equations
    - Had they sold . . .

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Be careful:   The post  (the solution)  by  @swincher4391  has an error !


Answer by MathTherapy(10551) About Me  (Show Source):
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lauren purchased a box of burgers for 35$ at her usual grocery store. When she got back home she saw a flyer for a different store advertising a price that was 50 cents less per burger. if laura has shopped at the second store she could have bought 8 more burgers for the same price
what was the price of one of the burgers lauren bought?
Let price of each burger be B
Then we get: matrix%281%2C3%2C+35%2FB%2C+%22=%22%2C+35%2F%28B+-+.5%29+-+8%29
matrix%281%2C3%2C+35%28B+-+.5%29%2C+%22=%22%2C+35B+-+8B%28B+-+.5%29%29 ------- Multiplying by LCD, B(B - .5)
matrix%281%2C3%2C+35B+-+17.5%2C+%22=%22%2C+35B+-+8B%5E2+%2B+4B%29
matrix%281%2C3%2C+8B%5E2+-+4B+-+35B+%2B+35B+-+17.5%2C+%22=%22%2C+0%29
matrix%281%2C3%2C+8B%5E2+-+4B+-+17.5%2C+%22=%22%2C+0%29
matrix%281%2C3%2C+16B%5E2+-+8B+-+35%2C+%22=%22%2C+0%29 --------- Multiplying by 2 to CLEAR DECIMAL
matrix%281%2C3%2C+16B%5E2+-+28B+%2B+20B+-+35%2C+%22=%22%2C+0%29
4B(4B - 7) + 5(4B - 7) = 0
4B - 7 = 0 OR 4B + 5 = 0
Cost of a burger, or highlight_green%28matrix%281%2C5%2C+B%2C+%22=%22%2C+7%2F4%2C+or%2C+%22%241.75%22%29%29 OR matrix%281%2C4%2C+B%2C+%22=%22%2C+-+5%2F4%2C+%22%28ignore%29%22%29