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In following series find 20th number. ...

In following series find 20th number.
`9, 5, 1, -3, -7, -11, ........`

A

`-67`

B

`-64`

C

`-75`

D

`-70`

Text Solution

Verified by Experts

The correct Answer is:
A
`5 - 9 = -4 `
`1-5 = -4`
`-3 -1 = -4`
`-7 -(-3) = -4 `
The difference between consecutive terms is always – 4.
Therefore, nth term `= x_n = -4n+ z`
(Where z is an unknown number)
For, n= 1, `x_1 = 9`
` 9 = -4 xx1 +z`
`implies z = 9 + 4 = 13`
`:. x_(20) =-4 xx 20 + 13`
`=-80 + 13 =-67`
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