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The sum of `25` terms of an `A.P.`, whose all the terms are natural numbers, lies between `1900` and `2000` and its `9^(th)` term is `55`. Then the first term of the `A.P.` isA. `5`B. `6`C. `7`D. `8` |
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Answer» Correct Answer - C `(c )` Let the first term be `a` and the common difference `d`. Then it is given that `a+8d=55` and ……..`(i)` `1900 lt (25)/(2)(2a+24d) lt 2000` `:.1900 lt 25(a+12d) lt 2000` `implies1900 lt 25(a+8d)+25xx4d lt 2000` `implies1900 lt 25xx55+100d lt 2000` `implies(525)/(100) lt d lt (625)/(100)` `impliesd=6` as `d` is an integar `:. a=55-8xx6=7` |
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