Question

A youth group is selling snacks to raise money to attend their convention. Amy sold 2 pounds of candy, 3 boxes of cookies and 1 can of popcorn for a total sale of $65. Brian sold 4 pounds of candy, 6 boxes of cookies and 3 cans of popcorn for a total sale of $140. Paulina sold 8 pounds of candy, 8 boxes of cookies and 5 cans of popcorn for a total sales of $250. What is the cost of each item

Answer 1

Answer:

The cost of a can of popcorn is $10.

The cost of a box of cookies is $5.

The cost of a can of popcorn is $20

Step-by-step explanation:

First you must propose a system of equations, a set of two or more equations with several unknowns in which you want to find the value of each unknown so that all the equations of the system are fulfilled.

Defining the variables:

• x: cost of one pound of candy
• y: cost of a box of cookies
• z: cost of a can of popcorn

Amy sold 2 pounds of candy, 3 boxes of cookies and 1 can of popcorn for a total sale of $65. Then:

2*x + 3*y + 1*z=65 Equation 1

Brian sold 4 pounds of candy, 6 boxes of cookies and 3 cans of popcorn for a total sale of $140. So:

4*x + 6*y + 3*z=140 Equation 2

Paulina sold 8 pounds of candy, 8 boxes of cookies and 5 cans of popcorn for a total sales of $250. Then:

8*x + 8*y + 5*z=250 Equation 3

Then the system of equations is formed by these three equations.

A method to solve a system of equations is by means of the substitution method, which consists of isolating one of the two unknowns in an equation to substitute it in the other equation.

Isolating z from Equation 1:

$z=65-2*x-3*y$ Equation 4

Replacing in Equation 2:

4*x + 6*y + 3*(65 -2*x-3*y)=140

4*x + 6*y + 195 - 6*x  - 9*y= 140

-2*x - 3*y=140-195

-2*x - 3*y=-55

2*x + 3*y= 55

and isolating x:

$x=\frac{55-3*y}{2}$ Equation 5

Replacing in Equation 4:

$z=65-2*\frac{55-3*y}{2} -3*y$

z=65 - (55-3*y) - 3*y

z= 65 -55 + 3*y - 3*y

z= 10

So the cost of a can of popcorn is $10.

Replacing equation 5 and the value of z in equation 3:

8*$\frac{55-3*y}{2}$ + 8*y + 5*10=250

$\frac{8}{2}$*(55 -3*y)+ 8*y + 5*10=250

4*(55 -3*y)+ 8*y + 5*10=250

4*55 - 4*3*y + 8*y + 50=250

220 - 12*y + 8*y + 50=250

-12*y + 8*y= 250 -220 - 50

-4*y= -20

$y=\frac{-20}{-4}$

y= 5

So the cost of a box of cookies is $5.

Finally replacing the value of y in Equation 5 you get the value of x:

$x=\frac{55-3*5}{2}$

$x=\frac{55-15}{2}$

$x=\frac{40}{2}$

x=20

Finally, the cost of a can of popcorn is $20