Solution:
Three digit numbers here are 100 to 990 and the numbers which are divisible by 7 will be then given by:
105, 112, 119, 126, …, 994
Here, a = 105, d= 7, l = 994
Tn = (l) = a + (n – 1) d
⇒ 994 = 105 + (n – 1) x 7
⇒ 994 – 105 = (n – 1) 7
⇒ (n – 1) x 7 = 889
⇒ n – 1 = 127
⇒ n = 127 + 1 = 128
Required numbers is 128.