SQUARE OF A NUMBER WITH 5 IN ITS UNITS PLACE.

Here is a simple way to mentally calculate the square of numbers like 15,25,35 ....105 ...

EXAMPLE 1

Let us consider 15 :

Step 1. Take 5 from the units place and multiply it by 5 to get 25. 

Write down  25, which a part of the  answer.

Step 2. Take 1 which is to the left of 5.  The next higher number to 1 is 2.

Step 3. Multiply 1x2 to get 2.

Step 4. Write this  2, to the left of 25  which we wrote in step 1, to get 225, which is the final answer. 

15x15=225

 

EXAMPLE 2

Let us consider 25 :

Step 1. Take 5 from the units place and multiply it by 5 to get 25. 

Write down  25, which a part of the  answer.

Step 2. Take 2 which is to the left of 5. The next higher number to 2 is 3.

Step 3. Multiply 2x3  to get 6.

Step 4. Write this  6, to the left of 25  which we wrote in step 1, to get 625, which is the final answer. 

25x25=625

EXAMPLE 3

Let us consider 45 :

Step 1. Take 5 from the units place and multiply it by 5 to get 25. 

Write down  25, which a part of the  answer.

Step 2. Take 4 which is to the left of 5.  The next higher number to 4 is 5.

Step 3. Multiply  4x5  to get 20.

Step 4. Write this  20, to the left of 25  which we wrote in step 1, to get 2025, which is the final answer. 

45x45=2025

EXAMPLE 4

Let us consider 115 :

Step 1. Take 5 from the units place and multiply it by 5 to get 25. 

Write down  25, which a part of the  answer.

Step 2. Take 11 which is to the left of 5.  The next higher number to 11 is 12.

Step 3. Multiply 11x12  to get 132.

Step 4. Write this  132, to the left of 25  which we wrote in step 1, to get 13225, which is the final answer. 

115x115 =13225.

 

Practice frequently with different numbers so that you are able to this with ease.

   

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