3 digits numbers divisible by 7 are: 105, 112, 119, ……, 994 This is an arithmetic progression series in which first term, a = 105, difference, d = 7 and last term Tn = 994 ⇒ Tn = a + (n – 1) × d ⇒ 994 = 105 + (n – 1) × 7 ⇒ (n – 1) × 7 = 889 ⇒ n – 1 = 127 ∴ n = 128 three digits numbers are divisible by 7