College

A store sells almonds for [tex]\$ 7[/tex] per pound, cashews for [tex]\$ 10[/tex] per pound, and walnuts for [tex]\$ 12[/tex] per pound. A customer buys 12 pounds of mixed nuts consisting of almonds, cashews, and walnuts for [tex]\$ 118[/tex]. The customer buys 2 more pounds of walnuts than cashews.

The matrix below represents this situation:

[tex]
\left[\begin{array}{ccc|c}
0 & -1 & 1 & 2 \\
7 & 10 & 12 & 118 \\
1 & 1 & 1 & 12
\end{array}\right]
[/tex]

If the reduced row echelon form of this matrix represents the amount of each type of nut the customer buys, which statement is a possible interpretation of the results?

A. The customer buys 1 more pound of walnuts than almonds and 1 more pound of almonds than cashews.

B. The customer buys 2 more pounds of walnuts than almonds and 2 more pounds of almonds than cashews.

C. The customer buys 0.5 more pound of walnuts than almonds and 2.5 more pounds of almonds than cashews.

D. The customer buys 6.5 more pounds of walnuts than almonds and 8.5 more pounds of almonds than cashews.

Answer :

Let's analyze the problem with the information provided. We need to determine how many pounds of almonds, cashews, and walnuts the customer buys, given the conditions.

### Given Conditions:

1. Price per pound:
- Almonds cost \[tex]$7 per pound.
- Cashews cost \$[/tex]10 per pound.
- Walnuts cost \[tex]$12 per pound.

2. Total weight and cost:
The customer buys a total of 12 pounds of mixed nuts for \$[/tex]118.

3. Relationships between types of nuts:
The customer buys 2 more pounds of walnuts than cashews.

### Setting up the Problem:

To set up the problem, let's define variables for the amounts in pounds:
- [tex]\( a \)[/tex] = pounds of almonds
- [tex]\( c \)[/tex] = pounds of cashews
- [tex]\( w \)[/tex] = pounds of walnuts

#### Formulating Equations:

1. From the relationship between walnuts and cashews:
[tex]\[
w = c + 2
\][/tex]

2. From the total weight:
[tex]\[
a + c + w = 12
\][/tex]

3. From the total cost:
[tex]\[
7a + 10c + 12w = 118
\][/tex]

### Solve the System of Equations:

Using the equations, we can substitute [tex]\( w \)[/tex] in the second and third equations:

1. Substitute [tex]\( w = c + 2 \)[/tex] into [tex]\( a + c + w = 12 \)[/tex]:
[tex]\[
a + c + (c + 2) = 12 \\
a + 2c + 2 = 12 \\
a + 2c = 10 \tag{Equation 1}
\][/tex]

2. Substitute [tex]\( w = c + 2 \)[/tex] into [tex]\( 7a + 10c + 12w = 118 \)[/tex]:
[tex]\[
7a + 10c + 12(c + 2) = 118 \\
7a + 10c + 12c + 24 = 118 \\
7a + 22c = 94 \tag{Equation 2}
\][/tex]

Now solve Equation 1 and Equation 2 simultaneously:

From Equation 1:
[tex]\[ a = 10 - 2c \][/tex]

Substitute [tex]\( a = 10 - 2c \)[/tex] into Equation 2:
[tex]\[
7(10 - 2c) + 22c = 94 \\
70 - 14c + 22c = 94 \\
8c = 24 \\
c = 3
\][/tex]

Find [tex]\( a \)[/tex] from [tex]\( a = 10 - 2c \)[/tex]:
[tex]\[
a = 10 - 2(3) = 4
\][/tex]

Find [tex]\( w \)[/tex] from [tex]\( w = c + 2 \)[/tex]:
[tex]\[
w = 3 + 2 = 5
\][/tex]

### Conclusion:

The customer buys:
- 4 pounds of almonds
- 3 pounds of cashews
- 5 pounds of walnuts

Therefore, none of the given options correctly describe the relation between the amounts of the types of nuts the customer buys based on the solution.