# Easy Number System Solved QuestionAptitude Discussion

 Q. $(AA)^2 = DCBA$, where $A$, $B$, $C$ and $D$ are distinct digits with $B$ being odd. Find the value of $D$.
 ✔ A. 4 ✖ B. 6 ✖ C. 1 ✖ D. 1 or 4

Solution:
Option(A) is correct

Check the digits $A =1,2,3,4,......9$

$11 \times 11= 121$ (Not valid, only 3 digit number)

$22 \times 22= 484$ (Not valid, only 3 digit number)

$33 \times 33= 1089$ (Not valid, $B$ is NOT odd)

$44 \times 44= 1936$ (NOT valid since digit $A$ is not $4$ on the ridht hand side - unit's place)

$55 \times 55= 3025$ (Not valid, $B$ is NOT odd)

$66 \times 66= 4356$ (Valid choice, keep note of it)

$77 \times 77= 5929$ (Not valid, digits are NOT distinct)

$88 \times 88= 7744$ (Not valid, digits are NOT distinct)

$99 \times 99= 9801$ (Not valid, $B$ is NOT odd)

So we see that, only $66 \times 66= 4356$ satisfy the criteria.

Hence, $D =\textbf{4}$

Alternative Solution:

Note that for a perfect square number with ten's place odd, unit's place of the number must be 6.
$66×66 = 4356$.

also $44 \times 44=1936$ B is odd in both the cases.

But in the second case unit's digit on the right hand side is not $4$ ($44 \times 44 = DCB4$). So this option is NOT valid.

Then $D =\textbf{4}$

## (11) Comment(s)

P V Ashok
()

AA*AA should give DCBA 66*66 = 4356.....where does 44*44 give 4 in the unit's digit of answer?

Deepak
()

Solution has been modified as per your point. Correct answer choice has been pointed out as well.

Deep
()

As per question , unit digit should be same as the digits multiplied .

if we multiply 44 x 44 , we donot get unit digit as 4 in the solution

Deepak
()

Thank you for notifying the anomaly. Solution has been modified.

Buggi
()

the answer would be A (4)

Sahil
()

yeah i agree...

'A'whether in left side or in right side both should have same values i.e 6

if u make L.H.S (88*88 or 44*44) then in R.H.S also A will have the same value

i.e 4 or 8

rather it should have been E instead of A on R.h.s then ans then the ans. would have been 1 or 4

Niket
()

The answer can only be 4 as the case of 66 is valid since the last digit of the answer should be same as the left side i.e A

Niket
()

the answer can only be 4 since the last digit of the answer Should also be A so only the case of 6 is valid

Narendra Singh
()

As question says $(AA*AA)=DCBA$ then unit digit must be same i.e. A.

So only 1 solution which would satisfy this equation will be $66*66= 4356$. Here unit digit is same at both place i.e. 6 and 10th digit is Odd so correct answer would be 4.

Option 'A' should be the correct answer.

I think most of the person missed this point.

Please do change in solution which u have provided.

Robin Dhingra
()

According to me the answer would be all the options because square of $44=1936$ $66=4356$ and $88=6776$ also satisfies the conditions.

So the value of $d$ could be 1 4 or 6 also.

Ashita
()

According to me the answer to this question must be $D$ ie 1 or 4..

Since square of 44 is 1936 ie $B=3$ and $D=1$