GMAT Math

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.

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

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...

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

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...)

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

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….

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?

NO
though i wish it would be

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.

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.

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

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!