Question

If 18, X, Y, −3 are in AP, then the value of X + Y is

A) 12 B) 15

C) 16 D) 11
please give me explanation too ​

Answer 1

Answer: (B) 15

Explanation:

Here, a = 18

a-n = - 3

We know,

a-n = a + (n - 1)d

∴ - 3 = 18 + (4 - 1)d

[n = 4th term]

=> 3d = - 3 - 18 = - 21

=> d = - 7.

So, a-2 = X = 18 + 1.-7 = 11

Similarly, a-3 = Y = 18 + 2.-7 = 4.

Hence, X + Y = 11 + 4 = 15.

Answer 2

Answer:

15.

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