how many 4 - digit numbers are completely divisible by 7 ?
"solution : 4 - digit numbers divisible by 7 are : 1001 , 1008 , 1015 … . . 9996 . this is an a . p . in which a = 1001 , d = 7 , l = 9996 . let the number of terms be n . then tn = 9996 . . ' . a + ( n - 1 ) d = 9996 = > 1001 + ( n - 1 ) 7 = 9996 = > ( n - 1 ) 7 = 8995 = > ( n - 1 ) = 8995 / 7 = 1285 = > n = 1286 . . ' . number of terms = 1286 . answer b"
add(multiply(const_100, 4), const_100)