JAMB Mathematics 2018 Objective — Question 6
Question 6 of 39 from the Joint Admissions and Matriculation Board (JAMB) Mathematics 2018 Objective paper, with the correct answer and a full explanation.
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If the seventh term of an A.P is twice the third term and the sum of the first four terms is 42, find the common difference
- A. ½
- B. 2
- C. 3Correct
- D. 6
Explanation
T7=a+6d, T3=a+2d. a+6d=2(a+2d) → a=2d. S4=(4/2)(2a+3d)=42 → 2a+3d=21. Substituting a=2d: 7d=21 → d=3.
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