Latest self Aptitude Question SOLUTION: -20= -20 16-36 = 25- 45 4^2 - 9*4 = 5^2 - 9*5 Adding 81/4 on both sides 4^2 - 9*4 + 81/4= 5^2 - 9*5 + 81/4 4^2 - 5*9 + (9/2)^2 = 5^2 -5*9 + (9/2)^2 Now substituting the formula(

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(#M40009095) SELF question 2+2=5 Keep an EYE

-20= -20
16-36 = 25- 45
4^2 - 9*4 = 5^2 - 9*5
Adding 81/4 on both sides
4^2 - 9*4 + 81/4= 5^2 - 9*5 + 81/4
4^2 - 5*9 + (9/2)^2 = 5^2 -5*9 + (9/2)^2

Now substituting the formula( a-b)^2 we get 4-9/2 = 5-9/2
» 4=5
Or 2+2 = 5
I want to know where we are wrong????

sarvdeep malhan (12 years ago)

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Pargat Pal Singh  (12 years ago)

-20= -20
16-36 = 25- 45
4^2 - 9*4 = 5^2 - 9*5
Adding 81/4 on both sides
4^2 - 9*4 + 81/4= 5^2 - 9*5 + 81/4
4^2 - 5*9 + (9/2)^2 = 5^2 -5*9 + (9/2)^2

Now substituting the formula( a-b)^2
we also get
4-9/2 = -( 5-9/2)
4+5 = 9/2+9/2
9=9

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Pathak Praveen  (12 years ago)

look @ last two lines...
4^2 - 9*4 + 81/4= 5^2 - 9*5 + 81/4
4^2 - 5*9 + (9/2)^2 = 5^2 -5*9 + (9/2)^2
in 2nd line LHS 9*4 has been replaced by 5*9....
was it really a question or just limit of foolishness...

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Dolly  (12 years ago)

@ Pathak,

that is just a typing mistake.
-20= -20
16-36 = 25- 45
4^2 - 9*4 = 5^2 - 9*5
Adding 81/4 on both sides
4^2 - 9*4 + 81/4= 5^2 - 9*5 + 81/4
4^2 - 2*4*9/2 + (9/2)^2 = 5^2 -2*5*9/2 + (9/2)^2

Now substituting the formula( a-b)^2 we get 4-9/2 = 5-9/2


I think PP Singh has given valid logic for explaining the error in calculations.

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Balakrishnan M  (12 years ago)

20= -20
16-36 = 25- 45
4^2 - 9*4 = 5^2 - 9*5
Adding 81/4 on both sides
4^2 - 9*4 + 81/4= 5^2 - 9*5 + 81/4
4^2 - 4*9 + (9/2)^2 = 5^2 -5*9 + (9/2)^2

Now substituting the formula( a-b)^2
(4-9/2)^2=(5-9/2)^2==>(-0.5)^2=(0.5)^2
It is correct.
But,(4-9/2)=(5-9/2) is Wrong.
generall we can write, a=b implies a^2 = b^2.
but, a^2=b^2 doesnot implies a=b.
for example, (-2)^2 = 2^2
but We cannot write,-2 = 2.
so we cannot take (4-9/2)^2=(5-9/2)^2 is (4-9/2) =(5-9/2).

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Guhan S  (12 years ago)

-20= -20
16-36 = 25- 45
4^2 - 9*4 = 5^2 - 9*5
Adding 81/4 on both sides
4^2 - 9*4 + 81/4= 5^2 - 9*5 + 81/4
4^2 - 2*4*9/2 + (9/2)^2 = 5^2 -2*5*9/2 + (9/2)^2

Now substituting the formula( a-b)^2 we get (4-9/2)^2 = (5-9/2)^2

I think Balakrishnan given valid reason for the calculation mistake

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