In such cases, number of zeros equal to number of 9s in (10n -1) are put extreme right of N to make a new number M and then N is subtracted from this new number to get the result. Clearly, (M - N) is the result of multiplication.
Example- Multiply 6243 with 999.
Solution. Here, N=6243, (10n 1)=(103 -1) = 999
According to the rule,
(N) (M) (N)
6243*999=6243000 - 6243
999 has three 9s and hence
Three zero are put at the right
End of N to make M.
N is subtracted from M
To get the result