Multiplication of Numbers With a Series of 9's

Everyone know that 9 is the biggest number among all one digit numbers.

If i asked You to do the following exercise in just 5seconds.Can you do it?

Can Notice That It is not one type.It is of 3 types.

1.No.of Digits in 1st Number is equal to no.of 9's

2.No.Of Digits in 1st Number is less than no. Of 9's

3.No. of digits in 1st Number is greater than no. Of 9's

Algorithm:

For Type(1):(Multiply a Number with an equal number of nines)

Ex: 654×999

1. Subtract 1 From the 654 and write as left part of the answer.

2.Now subtract the left Part of the answer from 999 and place as right part of the answer.

For Type(2):(Multiply a Number with higher number of nines)

Ex:45×999

1.Make eual digits as per the  numer of nines.

2.Do as before explained.

And Finally The last case is 

Type(3)(Multiply a Number With a lower number of nines)

1.Instead of Multiplying 99 we can do it as (100-1)

2.Subtract that number from the result.

Hope You will Remember it.