Which term of the series 72, 63, 54, ....... is zero?

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Which term of the series 72, 63, 54, ....... is zero?

1. 11th
2. 10th
3. 9th
4. 8th

Correct Option: C

Here, a = 72 , d = 63 - 72 = – 9 , a_n = 0
Using the given formula ,
∴ a_n = a + (n – 1)d
⇒ 0 = 72 + (n – 1) × –9
⇒ 72 = 9 (7 – 1)
⇒ n – 1 = 8
⇒ n = 9