A pupil solves $4-3x\leq10$ and obtains $-3x\leq6$, then writes $x\leq-2$. Identify the error

Question

A pupil solves $4-3x\leq10$ and obtains $-3x\leq6$, then writes $x\leq-2$. Identify the error and give the correct solution.[2] Use $x=0$ to show that the pupil’s final inequality is not equivalent to the original inequality.[1]

Accepted Answer

(a) Reverse the sign when dividing by $-3$; $x\geq-2$ (b) $0$ satisfies the original inequality but not $x\leq-2$.

Checking an inequality method

Checking an inequality method

Solution:

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