Question

The middle most term(s) of the AP: -11, -7, -3,.... 49 is ______.

Options

• 18, 20

• 19, 23

• 17, 21

• 23, 25

Answer 1

The middle most term(s) of the AP: -11, -7, -3,.... 49 is 17, 21.

Explanation:-

Here, a = -11

d = -7 - (-11) = 4

And a_n = 49

We have,

a_n = a + (n - 1)d

⇒ 49 = -11 + (n - 1)4

⇒ 60 = (n - 1)4

⇒ n = 16

As n is an even number, there will be two middle terms which are `16/2"th"` and `[16/2+1]"th,"` i.e. the 8th term and the 9th term.

a₈ = a + 7d = -11 + 7 × 4 = 17

a₉ = a + 8d = -11 + 8 × 4 = 21