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2015-05-06T03:37:03+05:30

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Let the series be  a ,  a+d,  a+2d , .....
sum of the first 9 terms:    [2 a + 8 d] * 9/2 = 9 a + 36 d

   so  200 <= 9 a + 36 d <= 220

2nd term :  a + d = 12      =>  9a = 9 (12 - d) = 108 - 9 d

 =>  200 <= 108 - 9d + 36 d <= 220
  =>    92 <=  25 d <= 112
  =>     3.6 <=  d  <=  4.4

   => d = 4      as d is a natural number and  a is also a natural number.
   =>  a = 12 - 4 = 8.

series:  8, 12, 16, 20, 24, ...          sum of the first 9 numbers: 216

2 4 2
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