Aptitude - Numbers - Discussion
Discussion Forum : Numbers - General Questions (Q.No. 5)
5.
1397 x 1397 = ?
Answer: Option
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:
55 comments Page 2 of 6.
Dr R Vasudevan said:
1 decade ago
An easier method:
1397 is slightly less than 1400
1397*1397 must be slightly less than 1400*1400 = 1960000
There are only 2 numbers less than 1960000
i.e [A] 1951609 ; [C]. 18362619
[C] is too small. Hence the correct answer is (A).
Another check : tens digit : 7*7= 49 : unit digit 9, carry to tens digit 4; 7*9 = 7*9 +4 = 130 : 0 in Tens digit and 13 carried to Hundreds: (A) has 0 in Tens digit.
1397 is slightly less than 1400
1397*1397 must be slightly less than 1400*1400 = 1960000
There are only 2 numbers less than 1960000
i.e [A] 1951609 ; [C]. 18362619
[C] is too small. Hence the correct answer is (A).
Another check : tens digit : 7*7= 49 : unit digit 9, carry to tens digit 4; 7*9 = 7*9 +4 = 130 : 0 in Tens digit and 13 carried to Hundreds: (A) has 0 in Tens digit.
G.Sravani said:
1 decade ago
1397*1397 = 7*7=49
7*9=63
7*3 = 21
.......779
9*7 =63
9*9 = 81
3*7 = 21
.....779
.... 73
.....1
== 609
In option A contain last three digits as 609.
So Answer is " A "
7*9=63
7*3 = 21
.......779
9*7 =63
9*9 = 81
3*7 = 21
.....779
.... 73
.....1
== 609
In option A contain last three digits as 609.
So Answer is " A "
Satish reddy said:
1 decade ago
1397 is slightly less than 1400.
1397*1397 must be slightly less than 1400*1400 = 1960000.
There are only 2 numbers less than 1960000.
i.e [A] 1951609 ; [C]. 18362619.
[C] is too small. Hence the correct answer is (A).
1397*1397 must be slightly less than 1400*1400 = 1960000.
There are only 2 numbers less than 1960000.
i.e [A] 1951609 ; [C]. 18362619.
[C] is too small. Hence the correct answer is (A).
Rahul jadhav said:
1 decade ago
If you want to multiply this type of big no follow the step:
1397 * 1397 = ?
1397*1400 = 1955800.
and (1397+3 = 1400) So 1397*3 = 4191.
1955800-4191 = 1951609.
1397 * 1397 = ?
1397*1400 = 1955800.
and (1397+3 = 1400) So 1397*3 = 4191.
1955800-4191 = 1951609.
Sonal said:
1 decade ago
@Sravani.
How can you calculate the number of 779?
Can you explain it again?
How can you calculate the number of 779?
Can you explain it again?
Prashant said:
1 decade ago
Shortcut: Digital sum (D. S) method i.e 4.
D.S of 1397 is 2, so 1397*1397 is 2*2 = 4.
Now out of all the options the D.S of option a is 4.
D.S of 1397 is 2, so 1397*1397 is 2*2 = 4.
Now out of all the options the D.S of option a is 4.
Thukki said:
9 years ago
In shortcut method:
Digital sum (D. S) method i.e 4.
D.S of 1397 is 2, so 1397*1397 is 2*2 = 4.
Now out of all the options, the D.S of option a is 4.
Digital sum (D. S) method i.e 4.
D.S of 1397 is 2, so 1397*1397 is 2*2 = 4.
Now out of all the options, the D.S of option a is 4.
Esai said:
9 years ago
Explain me about digit sum method.
Naresh said:
9 years ago
@Thukki.
Digital sum means?
Digital sum means?
Gore said:
9 years ago
@Tamil.
Your answer is perfect.
Your answer is perfect.
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