WAEC Mathematics 2015 Objective — Question 1
Question 1 of 50 from the West African Examinations Council (WAEC) Mathematics 2015 Objective paper, with the correct answer and a full explanation.
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If {x : 2≤x≤18; x ∈ integer} and 7+x ≡ 4 (mod 9), find the highest value of x.
- A. 2
- B. 5
- C. 15Correct
- D. 18
Explanation
Solving 7+x≡4(mod9) gives x≡-3(mod9)→6(mod9). Adding 9 repeatedly within the range 2-18 gives x=6 or x=15; the highest value is 15.
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