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InterviewSolution
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The number of terms of an A.P. is even, the sum of odd terms is 24, ofthe even terms is 3, and the last term exceeds the first by 10 1/2 find thenumber of terms and the series.A. 8B. 4C. 6D. 10 |
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Answer» Correct Answer - D Given, `a_(1),a_(2),a_(3),..` are terms of A.P `therefore(a_(1)+a_(2)+…+a_(p))/(a_(1)+a_(2)+…+a_(q))=(p^(2))/(q^(2))` `rArr(p/2[2a_(1)+(p-1)d])/(q/2[2a_(1)+(q-1)d])=(p^(2))/(q^(2))` or `(2a_(1)+(p-1)d)/(2a_(1)+(q-1)d)=p/q` or `[2a_(1)+(p-1)d]q=[2a_(1)+(q-1)d]p` or `2a_(1)(q-p)=d[(q-1)p-(p-1)q]` or `2a_(1)(q-p)=d(q-p)` or `2a_(1)=d` `therefore(a_(6))/(a_(21))=(a_(1)+5d)/(a_(1)+20d)=(a_(1)+10a_(1))/(a_(1)+40a_(1))=11/41` |
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