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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 9th term is 55. Then the first term of the A.P. is
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a
5
b
6
c
7
d
8
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Correct option is C
t9=55⇒a+8d=55S25=252[2a+24d]=25(a+12d)=25(55+4d) G. T1900<25(55+4d)<2000⇒21<4d<25⇒d=6⇒a=7Similar Questions
If the sum of first terms of an is , then the sum of squares of these terms is
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