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The ratio between 5th and 8th term of a sequence is 1:7. a)Find the ratio between 6th and 15th terms of the series. b) if 7th term is 10, what will be 22nd term?
Let t5=x and t8=7x
ie,   a+4d = x    ........(i)
and a+7d = 7x  ........(ii)
solving (i) and (ii) we get a = -7x  and d = 2x
hence t6= a + 5d
             = -7x + 10x
             = 3x
          t8 = a+7d
              =-7x + 14d
              = 7x

Hence t6/t8 = 3/7    
   


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