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Question

Find 21×23, using a suitable algebraic identity.
  1. 483

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Solution

The correct option is A 483
We know that,
21×23 can be written as (20+1)×(20+3)
So, using the algebraic identity, (x+a)×(x+b)=x2+(a+b)x+ab

Here, x=20,a=1,b=3
(20+1)×(20+3)=202+(1+3)×20+1×3
=400+80+3
=483

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