How many three-digit natural numbers are divisible by 7?

The first three-digit number which is divisible by 7 is 105 and the last three-digit number which is divisible by 7 is 994. This is an A.P. in which a=105, d=7 and l=994. Let the number of terms be n. Then tn=994.
The nth term of an A.P. is given by tn = a + (n-1)d
∴ 994 = 105 + (n-1)7
⇒ 994 - 105 = 7(n-1)
⇒ n-1 = 889/7
⇒ n-1 = 127
⇒ n = 127 + 1
⇒ n = 128
∴ There are 128 three-digit numbers which are divisible by 7.