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Q.

What is the square of the number 21?


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a

441

b

444

c

411

d

414 

answer is A.

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Detailed Solution

The given number is 21.
Now divide the provided number into two equal parts, one of which must be a multiple of 10, and the other must not.
⇒21= 20 + 1
Squaring the number,
⇒ (21) 2 = 20+1 2 ⇒ 20+1 20+1 ⇒20 20+1 +1 20+1 ⇒400+20+20+1 ⇒441  
The number 441 is therefore the square of 21.
Therefore, option 1 is correct.
 
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