Question

Amelia, Luis, Shauna, and Clarence used different approaches to solve the inequality

7.2b + 6.5 > 4.8b – 8.1.

Amelia started by subtracting 7.2b from both sides to get 6.5 > –2.4b – 8.1.
Luis started by subtracting 4.8b from both sides to get 2.4b + 6.5 < – 8.1.
Shauna started by subtracting 6.5 from both sides to get 7.2b > 4.8b – 14.6.
Clarence started by adding 8.1 to both sides to get 7.2b + 14.6 > 4.8b.
Which student’s first step was incorrect, and why?

Amelia’s, because the variable term must be isolated on the left side
Luis’s, because he flipped the inequality sign when he subtracted
Shauna’s, because she did not apply the subtraction property of equality properly
Clarence’s, because the terms he added together were not like terms

Answer 1

Luis’s, because he flipped the inequality sign when he subtracted

Explanation:

Given:

7.2b + 6.5 > 4.8b – 8.1.

Amelia started by subtracting 7.2b from both sides to get 6.5 > –2.4b – 8.1.

Amelia:

7.2b + 6.5 - 7.2b > 4.8b – 8.1 - 7.2b

6.5 > -2.4b - 8.1

Correct

Luis started by subtracting 4.8b from both sides to get 2.4b + 6.5 < – 8.1.

7.2b + 6.5 - 4.8b > 4.8b – 8.1 - 4.8b

2.4b + 6.5 > -8.1

Incorrect

Shauna started by subtracting 6.5 from both sides to get 7.2b > 4.8b – 14.6

7.2b + 6.5 - 6.5 > 4.8b – 8.1 - 6.5

7.2b > 4.8b - 14.6

Correct

Clarence started by adding 8.1 to both sides to get 7.2b + 14.6 > 4.8b.

7.2b + 6.5 + 8.1 > 4.8b – 8.1 + 8.1

7.2b + 14.6 > 4.8b

Correct