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If the 10th term of the sequence a, a - b, a -2b, a -3b, .... is 20 and the 20th term is 10,then the xth term of the series is
If the 10th term of the sequence a, a - b, a -2b, a -3b, .... is 20 and the 20th term is 10,then the xth term of the series is
1). 10 - x
2). 20 - x
3). 29 - x
4). 30 - x
1). 10 - x
2). 20 - x
3). 29 - x
4). 30 - x
This Question has 2 answers.
I have read it somewhere 30 - x is correct
$ a_{10} = a - 9b = 20 $
$ a_{20} = a - 19b = 10 $
$ (a - 9b) - (a - 19b) = 20 - 10 $
$ 10b = 10 $
$ b = 1 $
$ a - 9(1) = 20 $
$ a = 29 $
$ a_x = a - (x-1)b $
$ a_x = 29 - (x-1)(1) $
$ a_x = 29 - x + 1 $
$ a_x = 30 - x $
$ \text{Answer: } 30 - x $
$ a_{20} = a - 19b = 10 $
$ (a - 9b) - (a - 19b) = 20 - 10 $
$ 10b = 10 $
$ b = 1 $
$ a - 9(1) = 20 $
$ a = 29 $
$ a_x = a - (x-1)b $
$ a_x = 29 - (x-1)(1) $
$ a_x = 29 - x + 1 $
$ a_x = 30 - x $
$ \text{Answer: } 30 - x $
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