How many three-digit numbers are divisible by 7?
The series of three-digit numbers divisible 7 is,
105, 112, 119,…………. 994
So here first term (a) is 105
Since it is divisible by 7 the common difference will be 7
Let an = 994
an = a + (n-1) d
994 = 105 + (n-1) 7
889 = (n-1)7
127 = n-1
n = 128