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Aptitude - Area - Discussion

@ : Home > Aptitude > Area > General Questions - Discussion

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"We cannot solve our problems with the same thinking we used when we created them."
- Albert Einstein
9. 

The diagonal of a rectangle is 41 cm and its area is 20 sq. cm. The perimeter of the rectangle must be:

[A]. 9 cm[B]. 18 cm
[C]. 20 cm[D]. 41 cm

Answer: Option A

Explanation:

l2 + b2 = 41.

Also, lb = 20.

(l + b)2 = (l2 + b2) + 2lb = 41 + 40 = 81

(l + b) = 9.

Perimeter = 2(l + b) = 18 cm.
Krish said: (Sat, Aug 20, 2011 12:09:39 PM)    
 
How 81 came?
Mmmm said: (Tue, Dec 6, 2011 10:47:29 AM)    
 
How did you take 40 there ?
Sabir said: (Mon, Dec 12, 2011 03:30:54 PM)    
 
As u know hypotenuse^2 = base^2+ alt^2
Since √41 is the diagonal
l^2 + b^2 = 41
Also lb = 20 (Since area = 20)
Now we have to find 2(l+b) (Perimeter)
So remember the formula (a+b)^2 = a^2 + 2ab + b^2
So (l+b)^2 = l^2 + b^2 + 2lb
= 41+(2*20)
=81
Therefore, l+b = 9
Now perimeter = 2(l+b)
= 2*9
=18 cm
:)
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