WAEC 2012 Mathematics · Question 7
Solve the inequality:
Options
- A.m
- B.m
- C.m
- D.m
Answer: C. m
Explanation written with AI and checked against the answer key
Step 1: Clear the fractions. The denominators are 2, 4, 12 and 6, so the LCM is 12. Multiply every term by 12:
12(−m/2) − 12(5/4) ≥ 12(5m/12) − 12(7/6)
−6m − 15 ≥ 5m − 14
Step 2: Collect like terms. Add 6m to both sides and add 14 to both sides:
−15 + 14 ≥ 5m + 6m
−1 ≥ 11m
Step 3: Divide by 11. Dividing by a positive number does not change the direction of the inequality:
−1/11 ≥ m, which means m ≤ −1/11
Check: Take m = −1, which satisfies m ≤ −1/11.
- Left side: 1/2 − 5/4 = −3/4
- Right side: −5/12 − 7/6 = −5/12 − 14/12 = −19/12
- Is −3/4 ≥ −19/12? Since −9/12 ≥ −19/12, yes.
Tip: Always multiply by the LCM first to remove the fractions. The inequality sign only flips when you multiply or divide by a negative number. Here we divided by +11, so it stayed the same. Also, "−1 ≥ 11m" is the same as "m ≤ −1/11", so read it from the variable's side.
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