Aptitude - Numbers - Discussion

1397=1+3+9+7=20.
1397=1+3+9+7=20.

20*20=400=4+0+0=4.

From options
A) 1951609=1+9+5+1+6+0+9=31,
3+1=4.
4 = 4. Hence ANSWER.

Nice explanations. Thanks all.

@All.

Guys don't solve this in this way. Just add the digits
Question is 1397 X 1397.
add digits
1 + 3 + 9+ 7 = 20, add again 2 + 0 = 2
So it becomes 2 X 2 = 4.

Now check options and see which sum upto 4
A) 1951609 = 1 + 9 + 5 + 1 + 6 + 0 + 9 = 31, 3 + 1 = 4. So this is the answer.
B) 1981709 = 1 + 9 + 8 + 1 + 7 + 0 + 9 = 35, 3 + 5 = 8, wrong.
C) 18362619 = 1 + 8 + 3 + 6 + 2 + 6 + 1 + 9 = 36, 3 + 6 = 9,
D) 2031719 = 2 + 0 + 3 + 1 +7 + 1 + 9 = 23, 2 + 3 = 5.

How come 1400?

Very easy method, Thanks @Aruna.

The multiplication of sum of digits = the some of digits of the answer.
example = 24*6 = 144 =1+4+4 = 9.
now 2+4 *6 = 36= 3+6=9.

So if the answer is given we can use this method.
Now, back to question.
1397*1397
1+3+9+7 * 1+3+9+7,
=2 * 2 = 4.
And, in option, 1951609 = 1+9+5+1+6+0+9 = 4.

1397 * 1397 = 1951609.

@Aruna.

Your method is perfect, Thanks.

1397*1397=?
1+3+9+7=20=2+0=2.
1+3+9+7=20=2+0=2.
2*2=4.

Option
A, 1951609 because
1+9+5+1+6+0+9=31=3+1=4 so it is the answer.

Thank you all for explaining the solution.