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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

Comments(21)

profileDeepak
2014-10-16 13:32:35 
Great but its trick doesn't follow (45879 x 999 = ?) this type simplification
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profileAniket
2015-11-19 12:29:06 
best way is 45879(1000-1)
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profileRaj
2014-07-10 19:33:34 
How to do this 12158 * 999 
Bz, 12158-1=12157

99999-12157=87842

Here ,right Answer is 12145842 ,where center value 45 How to get in answer ?
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profiles
2015-02-11 10:12:09 
When number of 9s are less than number of digit in other number The method is slightly different

here 12158*999 .It has 3 9's and other number has 5 digit

So divide the other number in to two group from right .Where right most group contain as much digit as number of 9s

that is 12158 to 2 group 12 and 158(because 3 9's)
then add 1 to the left group 12+1=13
now subtract this number from original number : 12158 - 13 = 12145

now take right most group 158 subtract it form 999+1 : 1000 - 158 = 842

So the result is combine this group 12145842

example 2

45612*999

45 and 612
45+1=46

45612 - 46 = 45566 => 1
1000 - 612 = 388 => 2

combine 1 and 2 => 45566388

example 3

4214*999

4 and 214

4214 - 5 = 4209
1000 - 214 = 786

so answer is 4209786
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profileAnuradha
2014-07-14 20:28:46 
I don't think this method can be used for problems like 12158 * 999 where number of digits > number of 9s

One method for such cases is 12158 * 999 = 12158(1000-1) = 12158000 - 12158 = 12145842
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profileMaruthu
2014-03-13 17:58:59 
8413*9999

1) 8413-1=8412
2)9999+1=10000-8413=1587

Ans: 84121587
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profileABDUL MUKEEM
2013-10-10 14:46:20 
758*99999
to solve these type of question 
there are 5 nines(9) so add zeros with digit 
as 
75800000
i added 5 zeros becoz of 5 times of nine(9)
now subtract digit from it
75800000-758=75799242 
this is the required ans.

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profilesunitha naidu
2016-02-17 05:21:37 
758*(100000-1)
75800000-758= 75799242
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profilehari
2013-09-18 09:12:48 
1.23458*999 =
2. 786*99=
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profileSANJAY PAUL
2015-09-15 12:19:30 
Just quick trick.
786*99

First take last 2 digit: 86
100 - 86 = 14
Write down at right : 14

Then add 1 to first digit :1+7=8
Then 786 - 8 = 778

Right answer is 77814
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