Question

The following is a student’s work when solving for y. There is a mistake in the work. What is the mistake? What is the correct answer? Explain. Step 1: P=2x+2y Step 2: P+2x=2y Step 3: P+2x2=y

Answer 1

Part 1

The mistake is Step 2: P + 2·x = 2·y

Part 2

The correct answer is

Step 2 correction: P - 2·x = 2·y

(P - 2·x)/2 = y

Explanation:

Part 1

The student's steps are;

Step 1; P = 2·x + 2·y

Step 2: P + 2·x = 2·y

Step 3: P + 2·x/2 = y

The mistake in the work is in Step 2

The mistake is moving 2·x to the left hand side of the equation by adding 2·x to P to get; P + 2·x = 2·y

Part 2

To correct method to move 2·x to the left hand side of the equation, leaving only 2·y on the right hand side is to subtract 2·x from both sides of the equation as follows;

Step 2 correction: P - 2·x = 2·x + 2·y - 2·x = 2·x - 2·x + 2·y = 2·y

∴ P - 2·x = 2·y

(P - 2·x)/2 = y

y = (P - 2·x)/2