Jane Street Interview Question: 37 times 37... | Glassdoor

# 37 times 37

5

Unless you're a whizz at computing the squares of two-digit numbers in your head, it's always easier to round one of the numbers up to a multiple of ten and add a correction. For example,

37 * 37 = 34 * 40 + 3^2

You can do 34*40 in your head much more easily than 37*37!

Anonymous on Mar 20, 2011
4

Or use multiple down and crosswise

7 * 7 = 49
3 * 7 + 3 * 7 + 4 (from 49) = 46
3 * 3 = 9 + 4 = 13(from 46)

1369

Anonymous on Apr 7, 2011
9

37 times 37 is 37 squared.

Rui on Jan 2, 2012
5

Hold on let me check my iPhone calc app.

Anonymous on Jan 5, 2012
8

Two ways:
37 * 37 = (40-3) * (40-3) = 40*40 - 6*40 + 9 = 1369

37 * 37 = (35+2)*(35+2) = 35*35 + 4*35 + 4
Any two digit number ending in 5 can be squared by taking tens digit, multiplying it by itself plus one, and tacking on a '25' at the end, so 35*35 = 1225
so 1225 + 140 +4 = 1369

John on Jan 10, 2012
7

This can be answered in well under 30 seconds by a simple application of quadratics.

37^2 = (30 + 7)*(30 + 7) = 30^2 + 7^2 + (2*30*7) = 900 + 49 + 420 = 1369

Anonymous on Jan 10, 2012
3

37^2

Anonymous on Jan 10, 2012
5

37373737373737373737373737373737373737373737373737373737373737373737373737

devsathish on Jan 10, 2012
0

I found it easy like this:
37 * 30 + 37*5 + 37*2 =
37*3*10 (1110) + 370/2 (185) + 74 = 1369

kisshoma on Jan 10, 2012
6

Question: " What is 37 times 37"

Rama on Jan 10, 2012
6

There is a mathematical "shortcut" for squaring any two digit number that would probably be the easiest to use:

1) Square the individual digits and place the results next to each other: 3^2=9 and 7^2=49 =&gt; 949
2) Multiply the two digits, double the result, and add a zero: 3*7=21 2*21=42 10*42=420
3) Add the two numbers: 949+420=1,369

Jake on Jan 10, 2012
1

Me: Approximately 1360.

Paul on Jan 10, 2012
1

37*40 - 37*3 = 1460 - 111 = 1369

Anonymous on Jan 10, 2012
1

Anonymous, I guess you meant:
37*40 – 37*3 = 1480 – 111 = 1369

MrCalc on Jan 10, 2012
3

I thought the agreement was that there was to be no math in this interview.

Charles Ellis Bruce on Jan 11, 2012
1

But do you like to golf? (intervention: redirection)

Not sure, on Jan 12, 2012
1

There are devices that can easily perform this sort of calculation. They're called calculators. If weren't aware of this I don't think I want to work for you.

Chris on Jan 14, 2012
1

Jane Street Capital is a heavy quant firm.

The point is that you are supposed to recognize 37 = (40-3)
and immediately expand its square to 40^2 +3^2- 2*3*40 which is very fast to
compute as 1600 + 9 - 240 = 1369

The point is whether you write down the expansion in less than 15 seconds and recognize that (40-3)^2 is easier to do by hand than (30+7)^2. People who are intrinsically comfortable with math do this .

Matt on Jan 19, 2012
2

A multiplication problem.

Jack on Jan 21, 2012
2

Takes his cell phone out.
Calculates the result.
Shows it to the interviewer without saying a word.

If they insist on calculating in your head or on paper, I'd say that it's too slow and I don't trust myself not to make an error when it comes to math. That's what computers are made for.

4

If the interview was for an accountant: "What do you want 37 times 37 to be?"

Fer on Feb 1, 2012
0

Use the trick for squaring numbers close to 50
37*37 = (25-13)*100 + 13^3 = 1200+169

Notice if you write
(50-13)(50-13) = 2500 - 100*13 + 13^2

Matt on Jul 1, 2013
0

Simple, 40 x 40 = 1600 ( easy to calculate on yr mind), 40- 37= 3, there are two 37's, means 2 x 3= 6, 6 x 40 = 240, so answer is 1600 - 240 = 1360 approximate.

Samuel binu on Dec 6, 2013
0

I always find adding numbers easier than subtracting them. So instead of (40-3)(40-3), I would prefer (30+7)(30+7) = 900 + 49 + 420 = 1369

Gaurav on Oct 1, 2015

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