Question 3

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

Solution

The given series is an arithmetic progression with first term $$a=9$$ and common difference $$d=-4$$

$$n^{th}$$ term in an A.P. = $$A_n=a+(n-1)d$$

=> $$A_{20}=9+(20-1)\times(-4)$$

= $$9+(19)(-4)$$

= $$9-76=-67$$

=> Ans - (D)

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In the following series find 20th number9, 5, 1, -3 -7, -11,........