Eduardo solved the following inequality, and his work is shown below:

Question

−5(x + 4) + 21 ≥ −3 + 4(x − 8)
−5x − 20 + 21 ≥ −3 + 4x − 32
−5x + 1 ≥ 4x − 35
−9x ≥ −36
x ≥ 4

What mistake did Eduardo make in solving the inequality?

Answer 1

When you multiply or divide by a negative number, you have to flip the inequality sign. So, Eduardo's final answer should be x ≤ 4.