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
answer is C.
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Detailed Solution
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=7