# Aptitude - Numbers - Discussion

Discussion Forum : Numbers - General Questions (Q.No. 5)
5.
1397 x 1397 = ?
1951609
1981709
18362619
2031719
None of these
Explanation:
 1397 x 1397 = (1397)2 = (1400 - 3)2 = (1400)2 + (3)2 - (2 x 1400 x 3) = 1960000 + 9 - 8400 = 1960009 - 8400 = 1951609.
Discussion:
52 comments Page 1 of 6.

Shivam said:   2 years ago
1397 * 1000 = 1397000,
1397 * 300 = 419100,
1397 * 90 = 125730,
1397 * 7 = 9779.

1397000 + 419100 + 125730 + 9779 = 1951609.
(10)

Ashish Thakor said:   2 years ago
Thank you everyone for giving the best explanations.
(2)

Jyotirban Pandey said:   2 years ago
How did 1400 come?

Nikita said:   2 years ago

Pritam said:   3 years ago
Step-1: Do the sum of the digits of multiplicands then multiply both.
Step-2: If the number comes in two-digit add them.
Step-3: Add all the digits of answer untill it becomes a single digit number.
15^2 = 225
1+5 * 1+5 = 2+2+5
6 * 6 = 9
36 = 9
3+6 = 9
9 = 9

(1)

Sagar said:   4 years ago
@Aruna.

Easy, thanks for solving it.

Deepmars said:   4 years ago
Good explanation, thanks @Pramod.

Pramod said:   4 years ago
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.
(7)

Rishi said:   4 years ago
Nice explanations. Thanks all.

Chethan Prabhu said:   4 years ago
@All.

Guys don't solve this in this way. Just add the digits
Question is 1397 X 1397.
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.
(9)