Question

A student attempted to solve the system 5x + 2y = 10 and 10x + 2y = 1 by graphing. The graph and the conclusion are

below. What can you say about the student's work?
y
-10x + 2y = 1
5x + 2y = 10
The soluion is ().
O The solution is incorrect because the student did not correctly identify the intersection.
O The solution is correct and the lines are graphed correctly.
O The solution is correct, but the lines were graphed incorrectly.
O The solution is incorrect because the lines are not graphed correctly.

Answer 1

Option A: The solution is incorrect because the student did not correctly identify the intersection.

Explanation:

Solve by elimination method.

5x + 2y = 10; -10x + 2y = 1

Multiply the second equation by -1, then add the equations together.

(5x + 2y = 10)

-1 (-10x + 2y = 1)

Forms:

5x + 2y = 10

10x - 2y = -1

Add these equations to eliminate y.

15x = 9

Then solve 15x = 9 for x:

15x = 9

15/15 = 9/15 (Divide both sides by 15)

x = 3/5

Now that we've found x let's plug it back in to solve for y.

Write down the original equation:

5x + 2y = 10

Substitute 3/5 for x in:

5x + 2y = 10:

5(3/4)+2y=10

2y+3=10

2y+3-3=10+-3

2y=7

2y/2 = 7/2

y = 7/2

x = 3/5 and y = 7/2.

Comparing the identified answers to the one found by the students, it can be concluded that Option A: The solution is incorrect because the student did not correctly identify the intersection.