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 4 of 6.
Jay vaghela said:
1 decade ago
Where is come form 1400 ?
G.M.L.GENATUS said:
1 decade ago
Just take a nearest whole value.
Abi said:
1 decade ago
Hai tamil, your explanation is nice.
Malik said:
1 decade ago
Can someone make me understand this line = (1400)2 + (3)2 - (2 x 1400 x 3) ?
Madhu said:
1 decade ago
Just that is a formula:
(a-b)^2 = a^2 + b^2 + 2ab in the same way
(1400-3)^2 = 1400^2 + 3^2 + 2*1400*3
(a-b)^2 = a^2 + b^2 + 2ab in the same way
(1400-3)^2 = 1400^2 + 3^2 + 2*1400*3
Sapna said:
1 decade ago
Very good explanation sunil.
Sharon said:
1 decade ago
Dear Tamil your explanation is good.
But please explain me from where do that 3 comes?
But please explain me from where do that 3 comes?
Kriti said:
1 decade ago
Well, the given explanation is in the form of (a-b) ^2=a^+b^-2ab. Which is easier to solve.
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 "
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