MATHS TRICK 4

 Maths Trick 1 says how to multiply up to 20 x 20 in our head.
Here we can play more .
MATHS TRICK 4 says how to multiply up to 30 x 30

Example 1.         21 x 22 

(Here we take 20 as the base number as 10 in  Maths  Trick 1)

Base number - 20
21  =  20  + 1
22  =  20  + 2

Step 1 :  21      +1
              22      +2
( +1 is the difference between 21 and 20 and  +2 is the difference between 22 and 20)

Step 2  :   21 + 2    =  23   OR  22 + 1 = 23  (CROSS SUM)

Step 3. :   23 x 20   = 460  (20 is the base number)

Step 4  :   1  x  2     =    2  

Step 5  : (Add 460 and 2)    460 +2  = 462  

Yes . That is the answer.

We can forget all these steps after getting it .

Example 2. 
                      23  x  24

Step 1 :     23  +  4   =  27
Step 2 :     27 x 20   =  540  ( short cut:  27 x 2 = 54, 27 x 20 = 540)
Step 3 :     3 x 4       =    12
Step 4 :    540 +12   = 552
                                   ===
Example 3
                    28 x 29

28 + 9   =    37
37 x 20 =    740       (37x2 =74 , 37 x 20 = 740)
8 x 9     =      72
740  +  72 =  812

Yes. That is the answer.

Example 4.
                   26 x 29

The multiplication must only be in your head

26 + 9 = 35 x 20 = 700 + 54 = 754
                                                 ===
Exercise

1.      22 x 25

2.      23 x 27

3.      24 x 29

4.      28 x 21

5.      25 x 29 

MATHS TRICK 3

An easy way to square any number  ending with 5
The way of squaring can be done like this:

Example  1 
                       15 ²  = 15 x 15  =225
        short cut : 
Step 1.  Separate the 5 from the  number to be squared        1    5   
Step 2. The remaining portion of the number is multiplied by the immediate higher number  1 x 2 =2
Step 3.  Suffix 25 to the result of   Step 2       =       225
 

Example 2.

                           25 ²            =  2     5
                                    2 x 3 =  6   25
                                             =  625

Example 3.                 35 ²   = 3 x 4 = 12 25
                                             = 1225
Example 4.                 85 ²   = 8 x9 = 72  25
                                             = 7225
Example 5          115 ²    = 11 x 12   ( Here we apply the Maths Trick 1)
                          11 + 2 = 13 0  +
                            1 x 2  =      2
                                         ------                            
                                          132

                         115 ² = 13225
                                                                        Maths can be fun ! 


 Example 6.      225 ²       = 22 x 23 (Short cut for this multiplication will be later)
                                         = 506
                         225 ²        = 506 25
                                         = 50625
                                            ====