Is calculator use permitted on the GMAT exam?

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markd4863: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Wed Dec 27, 2006 3:55 pm

by markd4863 » Fri Dec 29, 2006 10:36 am

I've read previously that, in fact, they are not allowed. But the official guide presents questions that seem virtually impossible to solve without the use of a calculator. For example...

Which fraction, if written as a repeating decimal, would have the longest sequence of different digits?

2/11 , 1/3 , 41/99 , 2/3 , 23/37

solved -

.1818... , .333... , .4141... , .666... , .621621...

can anyone confirm that calculators are not allowed, and how they would solve the above question without. thanks.

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Source: Beat The GMAT — Quantitative Reasoning | Fri Dec 29, 2006 10:36 am

aim-wsc: Legendary Member; Posts: 2469; Joined: Thu Apr 20, 2006 12:09 pmFollowed by: 14 members; Location: BtG Underground; Thanked: 85 times

by aim-wsc » Fri Dec 29, 2006 11:30 am

NO

NO IN CAPITAL BLOCK

you are not allowed to take calculator any gadgets infact not even a wrist watch with stop-watch

If you are seeing some Q problems that need tedious calculation, just know that its a tricky problem & you actually can solve it without even using calculator...
see for this (given ) example:

you can get the answer without doing that calculation

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aim-wsc: Legendary Member; Posts: 2469; Joined: Thu Apr 20, 2006 12:09 pmFollowed by: 14 members; Location: BtG Underground; Thanked: 85 times

Re: Is calculator use permitted on the GMAT exam?

by aim-wsc » Sat Apr 14, 2007 8:34 am

markd4863 wrote:
Which fraction, if written as a repeating decimal, would have the longest sequence of different digits?

2/11 , 1/3 , 41/99 , 2/3 , 23/37

solved -

.1818... , .333... , .4141... , .666... , .621621...

Some times you actually have to know number properties by heart.
for example 0.125 is nothing but 1/8.

No short cut or trick for this ( at least I dont know any ) but it'll be a lot easier if you are familiar with numbers. ... if you used to play with numbers...

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jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pmFollowed by: 1 member; Location: Silicon valley, California; Thanked: 30 times

Re: Is calculator use permitted on the GMAT exam?

by jayhawk2001 » Sat Apr 14, 2007 8:43 am

markd4863 wrote:I've read previously that, in fact, they are not allowed. But the official guide presents questions that seem virtually impossible to solve without the use of a calculator. For example...

Which fraction, if written as a repeating decimal, would have the longest sequence of different digits?

2/11 , 1/3 , 41/99 , 2/3 , 23/37

solved -

.1818... , .333... , .4141... , .666... , .621621...

can anyone confirm that calculators are not allowed, and how they would solve the above question without. thanks.

This has to be done with manual division (yes, on a piece of paper errr
a wet erase board).

The key here is to stop once you see a repeating digit after
the decimal point. As you can see only 3 options need actual division
beyond 2 decimal points. And if you are familiar with values for 1/3,
2/3, 1/11 etc. it becomes even simpler

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Stacey Koprince: GMAT Instructor; Posts: 2228; Joined: Wed Dec 27, 2006 3:28 pmFollowed by: 694 members; Location: Montreal, Canada; Thanked: 639 times; GMAT Score:780

by Stacey Koprince » Mon Apr 16, 2007 10:56 pm

There is an official math way to do this, yes, but it's messy (and I don't recommend it). If you care to learn:
https://en.wikipedia.org/wiki/Recurring_decimal

The easiest way to do this is to know 1/3 and 2/3 (and therefore know they aren't the right answer) and then do long division for the other 3. You only have to do the long division long enough to see how many places you have before it repeats. This is feasible within two minutes.

And, technically, after you see that options A and C each have a 2-digit repeater... you know E must be right without trying it, b/c there's only one right answer - A and C can't both be it. But you should probably still try E just to be sure.

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makoman: Newbie | Next Rank: 10 Posts; Posts: 1; Joined: Wed Jun 25, 2008 4:49 pm; Thanked: 4 times

by makoman » Wed Jun 25, 2008 4:54 pm

The trick is to multiply the denominator to a series of 9s

1/3 or 2/3 = 3/9 or 6/9 = .33333 or .99999

2/11 = 18/99 = .181818181818

41/99 = .414141414141

23/37 = 621/999 = .621621621621

If the denominator is all 9s, the repeating digit is just the numerator.

Hope this helps (other people that are now looking here...)

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dixitp_iitg: Newbie | Next Rank: 10 Posts; Posts: 1; Joined: Wed Sep 10, 2008 1:40 am

by dixitp_iitg » Wed Sep 10, 2008 1:56 am

One quick way is to find the largest Prime number denominator out of the options.

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GMATCHPOINT: Senior | Next Rank: 100 Posts; Posts: 51; Joined: Wed Oct 08, 2008 12:50 pm

by GMATCHPOINT » Thu Nov 27, 2008 9:07 am

I wanted to bring this discussion back, not because the question about calculator (we know this is not allowed during gmat), but for the fact that simple problems like this one here stated by markd4863 can get people terrible in math (like me) in serious trouble.

The method Stacey describes below is pretty much what I do when I face this sort of exercise (i.e. try to eliminate as much “obviously-wrong” answers, and move forward calculating the remaining options). However the reason I became curious when I found this thread is due to the last two posts. One of them says that one way to solve this would be to multiply the denominator to a series of 9s. The other says “…to find the largest Prime number denominator out of the options…”

I wondering if someone good with math could help me out with this. Maybe an instructor or any other experts like Logitech, Cramya and others….

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acon: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Wed Jan 20, 2010 10:46 pm

by acon » Wed Jan 20, 2010 11:16 pm

makoman wrote:The trick is to multiply the denominator to a series of 9s

1/3 or 2/3 = 3/9 or 6/9 = .33333 or .99999

2/11 = 18/99 = .181818181818

41/99 = .414141414141

23/37 = 621/999 = .621621621621

If the denominator is all 9s, the repeating digit is just the numerator.

Hope this helps (other people that are now looking here...)

Is there an easy way to find what multiple of your denominator will give you all nines?

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bhumika.k.shah: Legendary Member; Posts: 941; Joined: Sun Dec 27, 2009 12:28 amFollowed by: 1 member; Thanked: 20 times

by bhumika.k.shah » Thu Jan 21, 2010 6:59 am

though i wish it would be

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acon: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Wed Jan 20, 2010 10:46 pm

by acon » Thu Jan 21, 2010 11:43 am

The best I can figure is to use double division (search it in google).

Start by dividing into 99. If you get a remainder, add a nine up top, and then 0s and 9s where appropriate, and continue dividing your remainder until you have no remainder left.

See doubledivision.org

I don't know if you'd have to go into this depth on a test though.

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bedazzled: Senior | Next Rank: 100 Posts; Posts: 57; Joined: Fri Jan 22, 2010 11:25 am

by bedazzled » Mon Jan 25, 2010 12:55 am

makoman wrote:The trick is to multiply the denominator to a series of 9s

1/3 or 2/3 = 3/9 or 6/9 = .33333 or .99999

2/11 = 18/99 = .181818181818

41/99 = .414141414141

23/37 = 621/999 = .621621621621

If the denominator is all 9s, the repeating digit is just the numerator.

Hope this helps (other people that are now looking here...)

Its really good trick. Last week manhattan GMAT challenging problem was to find the 18th number in 1/37 on which I wasted 2 mins. or some. then too wrong answer. I should have simply multiplied 27 to numerator & denominator. I would hv got
027/999 = .027027027027027027
7 is answer here.

Thnx buddy.

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regor60: Master | Next Rank: 500 Posts; Posts: 416; Joined: Thu Oct 15, 2009 11:52 am; Thanked: 27 times

by regor60 » Tue Jan 26, 2010 12:17 pm

bedazzled wrote:
makoman wrote:The trick is to multiply the denominator to a series of 9s

1/3 or 2/3 = 3/9 or 6/9 = .33333 or .99999

2/11 = 18/99 = .181818181818

41/99 = .414141414141

23/37 = 621/999 = .621621621621

If the denominator is all 9s, the repeating digit is just the numerator.

Hope this helps (other people that are now looking here...)
Its really good trick. Last week manhattan GMAT challenging problem was to find the 18th number in 1/37 on which I wasted 2 mins. or some. then too wrong answer. I should have simply multiplied 27 to numerator & denominator. I would hv got
027/999 = .027027027027027027
7 is answer here.

Thnx buddy.

Shouldn't take more than 15 seconds with division ? Get .027 and see that it repeats, 6 reps gets 18 digits, 18th being 7, done

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Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members; Location: Montreal; Thanked: 1090 times; GMAT Score:780

by Ian Stewart » Tue Feb 02, 2010 6:19 pm

dixitp_iitg wrote:One quick way is to find the largest Prime number denominator out of the options.

Just in case it's confusing for anyone, the method suggested in the quoted text above will not normally work; if it does, it's pure coincidence. The fraction 1/7, for example, has a repeating pattern of six digits (1/7 = 0.142857142857....), whereas the fraction 1/11 has a repeating pattern of only two digits (1/11 = 0.090909...) despite having a larger prime denominator.

For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com

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Sarahcbl: Newbie | Next Rank: 10 Posts; Posts: 2; Joined: Wed Jul 13, 2011 9:03 pm

by Sarahcbl » Wed Jul 13, 2011 9:07 pm

The trick is to multiply the denominator to a series of 9s

1/3 or 2/3 = 3/9 or 6/9 = .33333 or .99999

2/11 = 18/99 = .181818181818

41/99 = .414141414141

23/37 = 621/999 = .621621621621

Why is the first answer not .666666 but .99999 when the answer to the rest is the numerator when the denominator is a series of 9s?

Thanks!

Last edited by Sarahcbl on Wed Jul 13, 2011 9:13 pm, edited 1 time in total.

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