Question

Which term of the AP 5, 8, 11, 14, .... is 320 ?
1. 103
2. 106
3. 105
4. None of these

Answer 1

Correct Answer - Option 2 : 106

Concept: 

Let us consider sequence a1, a2, a3 …. an is an A.P. 

Then nth term of AP is , 

Tn = Sn - Sn-1 

Common difference = d = Tn - Tn-1 

Calculation: 

Given: 5, 8, 11, 14, .... is an AP

Here, a = 5 and d = 3

Let the nth term of the given AP is 320

As we know that, if a is the first term and d is the common difference of an AP then an = a + (n - 1) × d

⇒ 320 = 5 + (n - 1) × 3

⇒ 320 = 5 + 3n - 3

⇒ 3n = 318

⇒ n = 106

Hence, correct option is 2.