How to multiply numbers near to 100

consider two numbers near to 100

e.g 97 and 98

Subtract  both these from 100

100-97 = 3
100 -98 = 2

Now add of them (3+2) = 5
Remove this from 100 i.e. 100-5 = 95

Now mutliply them 3 x 2 = 06

so the result will be 95 and append 06 => 9506

Let us take another example

92 x 97
100 -92 = 8
100-97 = 3

8+3 = 11, remove this from 100 i.e. 89
now multiply 8 x 3 = 24
so the answer is 8924

Try the below

1. 94 x 96
2. 99 x 91

Table 9 with hands

Instead of memorizing the table 9, use your hands to multiply

Face your palms as shown above

If you have to mutliply 9 x 3, fold the 3rd finger

if you check now, there will be two fingers on left side and 7 fingers on right side

keep the left value in tens and right value in ones i.e. 2 7

Let us take one more example 9 x 7, now fold the 7th finger, you will have now 6 fingers on left side and 3 fingers on right side so the value will be 6 3

Simple Trigonometry

Remember the above image and we can derive the below values easily

sin(0) = cos(90) = sin(180) = cos(270) =  sin(360) = cos(-90) = 0
cos(0) = sin(90) = 1
cos(180) = sin(270) = -1

sin(A + B) = sin A cos B + cos A sin B
cos(A + B) = cos A cos B − sin A sin B

sin(A − B) = sin A cos B − cos A sin B
cos(A − B) = cos A cos B + sin A sin B

Tip#2 : How to Multiply a number with 11 easily less than 5 seconds

How to Multiply a number with 11 easily

Tip: keeping the leftmost and right most numbers as is, add the numbers with its next number and put it in between leftmost and right most

Let us take an example of multiplying 25 with 11 

• Step 1 : keep 2 as is
• Step 2: add 2 and its next number i.e. 2 + 5 = 7
• Step 3: now keep 5 next to 7
• (2) (2+5) (5) = 275 is the answer

Another example:

• Multiply 159 with 11 = 159 x 11
• (1) (1+5) (5+9) (9) = (1) (6) (14) (9)
• Here 14 is having value more than 10, so this should be added to its previous number i.e. 6 in this scenario.
• (1) (6+1) (4) (9) = 1749 is the answer

One more example

• Multiply 4251 with 11
• (4) (2) (5) (1) 
• (4) (4+2) (2+5) (5+1) (1)
• (4) (6) (7) (6) (1)
• Answer is 46761

Try the following on your own:

43 x 11 = ?

923 x 11 = ?

4929 x 11 = ?

Feel free to write to me kosuru@gmail.com for any further help / suggestions

Tip#1 : Square a number ending with 5

Tip#1 : How to Square a number ending with 5

Let us take number 65 and we need to find a square of the same
Time Limit: 5 sec

1. Take out 5 out of the number i.e. we are left with 6
2. Take the next number of 6, which is 7
3. Now Multiply 6 with its next number i.e. 6 x 7 = 42
4. 5 square is 25
5. Now append 42 with 25 => 4225 (Four thousand and two hundred twenty five) 

Hope this tip will help you do the calculation simple.

want to try yourself: 

• Find square of 75 
• Find square of 125
• Find square of 105
• Find square of 45

ANSWERS below (scroll down)