WAEC Mathematics 2017 Theory — Question 7
Question 7 of 25 from the West African Examinations Council (WAEC) Mathematics 2017 Theory paper, with the correct answer and a full explanation.
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4. If the sixth term of an Arithmetic Progression (A.P.) is 37 and the sum of the first six terms is 147, find: (a) First term; (b) Sum of the first fifteen terms.
Model answer
U6=a+5d=37. Sn=(n/2)[2a+(n-1)d]: S6=(6/2)[2a+5d]=147 → 3(2a+5d)=147 → 2a+5d=49. Since a+5d=37, subtracting: a=49-37=12. Then 5d=37-12=25, d=5. (a) First term a=12. (b) S15=(15/2)[2(12)+(15-1)5]=(15/2)[24+70]=(15/2)(94)=705.
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