Multiplying any Number with 99, 999, 9999 etc using Speed Mathematics
Example 1

Calculate 24 * 99

Solution

1. Decrement one from the number. So here 24-1 = 23

2. Decrement each digit of the number obtained from 9. Here we got 23. Now 9-2 = 7 and 9-3=6. So we have 76

3. Just write these numbers together. That is we have 23 and 76. Hence answer is 2376

Example 2

calculate 2358 * 9999

Solution

1. Decrement one from the number. So here 2358-1 = 2357

2. Decrement each digit of the number obtained from 9. Here we got 2357. Now 9-2 = 7 , 9-3=6 , 9-5=4 and 9-7=2. So we have 7642

3. Just write these numbers together. That is we have 2357 and 7642. Hence answer is 23577642

Example 3

calculate 758 * 99999

Solution

1. Since the number of digits in 99999 is 5, we need to write 758 as 00758 in order to treat it as a 5 digit number

1. Decrement one from the number. So here 00758-1 = 00757

2. Decrement each digit of the number obtained from 9. Here we got 00757. Now 9-0=9, 9-0=9, 9-7=2, 9-5=4, 9-7=2. So we have 99242

3. Just write these numbers together. That is we have 00757 and 99242. Hence answer is 0075799242 or 75799242

 
 
 
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anonymous
2013-02-20 18:51:58 
What if the number of digits is less than the number of 9s? e.g. 6345*99
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