Which term of A.P. 72, 68, 64, 60, …., is 0 ?

In the A.P. 72, 68, 64, 60,…., a = 72 and d = 68 - 72 = -4.

Let n^th term be 0.

∴ a_n = 0

n^th term of an A.P. is given by,

a_n = a + (n - 1)d

⇒ 0 = 72 + (n - 1)(-4)

⇒ -72 = (n - 1)(-4)

⇒ n - 1 = $\dfrac{-72}{-4}$

⇒ n - 1 = 18

⇒ n = 18 + 1

⇒ n = 19.

Hence, 19th term of A.P. is 0.