High School

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]\[
\begin{array}{ccc|c}
0 & -1 & 1 & 2 \\
7 & 10 & 12 & 118 \\
1 & 1 & 1 & 12
\end{array}
\][/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 65 more pounds of walnuts than almonds and 8.5 more pounds of almonds than cashews.

Answer :

Let's solve the problem step-by-step using the information given:

1. Identify Variables:
- Let [tex]\( x \)[/tex] be the pounds of almonds.
- Let [tex]\( y \)[/tex] be the pounds of cashews.
- Let [tex]\( z \)[/tex] be the pounds of walnuts.

2. Set Up Equations:
- From the problem, we have the following conditions:

a. The total weight of the nuts is 12 pounds:
[tex]\[
x + y + z = 12
\][/tex]

b. The total cost of the nuts is $118:
[tex]\[
7x + 10y + 12z = 118
\][/tex]

c. The customer buys 2 more pounds of walnuts than cashews:
[tex]\[
z = y + 2
\][/tex]

3. Solve the Equations:
- We will use these three equations to find the values of [tex]\( x \)[/tex], [tex]\( y \)[/tex], and [tex]\( z \)[/tex].

- Substitute [tex]\( z = y + 2 \)[/tex] from (c) into equations (a) and (b):
[tex]\[
x + y + (y + 2) = 12
\][/tex]
Simplify:
[tex]\[
x + 2y + 2 = 12 \implies x + 2y = 10
\][/tex]

- Now substitute [tex]\( z = y + 2 \)[/tex] into equation (b):
[tex]\[
7x + 10y + 12(y + 2) = 118
\][/tex]
Simplify:
[tex]\[
7x + 10y + 12y + 24 = 118
\][/tex]
[tex]\[
7x + 22y = 94
\][/tex]

4. Solve the Simplified System:
- We have the system of equations:
[tex]\[
x + 2y = 10
\][/tex]
[tex]\[
7x + 22y = 94
\][/tex]

- Solve for [tex]\( x \)[/tex] in the first equation:
[tex]\[
x = 10 - 2y
\][/tex]

- Substitute [tex]\( x = 10 - 2y \)[/tex] into the second equation:
[tex]\[
7(10 - 2y) + 22y = 94
\][/tex]
Simplify:
[tex]\[
70 - 14y + 22y = 94
\][/tex]
[tex]\[
70 + 8y = 94
\][/tex]
[tex]\[
8y = 24
\][/tex]
[tex]\[
y = 3
\][/tex]

- Substitute [tex]\( y = 3 \)[/tex] back into [tex]\( x = 10 - 2y \)[/tex]:
[tex]\[
x = 10 - 2(3) = 4
\][/tex]

- Find [tex]\( z \)[/tex] using [tex]\( z = y + 2 \)[/tex]:
[tex]\[
z = 3 + 2 = 5
\][/tex]

5. Interpret the Results:
- The customer bought 4 pounds of almonds, 3 pounds of cashews, and 5 pounds of walnuts.

Based on the possible interpretations in the question, none of the given statements exactly match these results. However, with the correct results [tex]\( x = 4 \)[/tex], [tex]\( y = 3 \)[/tex], and [tex]\( z = 5 \)[/tex], we can understand the solution of the nut quantities purchased by the customer.