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Re: "Sometimes you just have to guess" - What Level is this? [#permalink]
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TIP If the denominator is 9, 99, 999 or another number equal to a power of 10 minus 1, then
the numerator gives you the repeating digits
:D
A) 2/11= 18/99 = 0.181818
B) 1/3 you should know that it is 0.333333333
C) 41/99 according to the tip above it should be 0.4141414141
D) 2/3 you should know that it is 0.66666666
E) 23/37 you solve then you see :D
it didn't take more than a minute
please consider giving me kudos if you see it was helpful in any way
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Which of the following fractions when expressed as repeating decimals [#permalink]
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Bunuel wrote:
Which of the following fractions when expressed as repeating decimals would have the longest sequence of different digits?

A. 2/11
B. 1/3
C. 41/99
D. 2/3
E. 23/37

if each of the following fractions were written as a repeating decimal, which would have the longest sequence of different digits?


A. 2/11 = 0.181818..... 2 repeating numbers after decimal
B. 1/3 = 0.3333.....1 repeating numbers after decimal
C. 41/99 = 0.41414.......2 repeating numbers after decimal
D. 2/3 = 0.666666.....1 repeating numbers after decimal
E. 23/37 = 0.621621..........3 repeating numbers after decimal...ANSWER!

P.S: Option C and E involved big numbers. So, for option C, I calculated 40/100 = 0.40...then assumed than since prime is divided by 99, the decimal answer would be closer to 0.40. Also, 99 which is 11*9 will always give non-terminating repeating decimal. 11 gives out 2 repeating decimals so 99 would do the same. The remaining and last suspect option was answer E = prime/prime. Even checked it by calculating.
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Re: PS - Number properties [#permalink]
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I cant think of anything shorter. But, the way I do it is
for 2/11. I make it 20/11. So the quotient will be 1.8181..Then I shift the decimal so it is 0.18

10/3 = 3.333 = 0.3
410/99 = 4.11 = 0.41
20/3 = 6.666 = 0.6
230/37 = 6.21621 = 0.621

So 23/37 has the longest sequence of digits
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Re: PS - Number properties [#permalink]
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walker wrote:
After reading of the problem I pick E by intuition: I thought that:
1. nominators do not influence on length of sequence. (for right fraction) - it is true
2.the largest prime in denominator lead to the largest sequence). - it is false


I think a fast way for such problem is:

1. Test for right fractions.
2. Exclude nominators
3. Exclude 2 and 5 from a denominators.
4. 3,9 - n=1, 3,11,33,99 - n=2
5. POI
6. find 1/denominator for remained variants.

For example,
A.3/22
B.5/198

1. ok
2. 1/22, 1/198
3. 1/11, 1/99
4. n=2, n=2
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Re: PS - repeating decimal [#permalink]
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E

1. reduce fraction if it is possible. Here we have all proper fractions.
2. because numerator does not influence on period of sequence, set all numerators to 1: 1/11, 1/3, 1/99, 1/3, 1/37
3. transform all fraction to the denominator such as 9, 99, 999 .....: 9/99, 3/9, 1/99, 3/9, 1/37
4. 1/37 we cannot write out as a fraction with denominator of 9 or 99. (actually we can with 999 but this is not necessary here) So, E is a winner.
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Re: If each of the following fractions were written as a repeati [#permalink]
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gmatraider wrote:
If each of the following fractions were written as a repeating decimal, which would have the longest sequence of different digits?

A) 2/11
B) 1/3
C) 41/99
D) 2/3
E) 23/37


If a fraction (in lowest terms) can be written as a repeating decimal and the number of decimal digits repeating is n, then the denominator must be a factor of 10^n - 1.

For example, 1/3 (in choice B) has a denominator of 3, which is a factor of 9 = 10^1 - 1 = 9; thus, 1/3 has 1 decimal digit repeating. Sure enough, 1/3 = 0.333… Another example, 2/11 (in choice A), has a denominator of 11, which is a factor of 99 = 10^2 - 1 = 99; thus, 2/11 has 2 decimal digits repeating. Sure enough, 2/11 = 0.181818…

Using this fact, we can see that 2/3 (in choice D) and 41/99 (in choice C) have 1 and 2 decimal digits repeating, respectively. Thus, the fraction 23/37 has the longest sequence of repeating decimal digits, since 37 is neither a factor of 9 nor a factor of 99. Regardless of the exact number of repeating decimal digits 23/27 has, it will certainly be more than 2.

Answer: E
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Re: Which of the following fractions when expressed as repeating decimals [#permalink]
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Answer is E

Trick: If a fraction consists of two co-prime numbers, then the larger the denominator, the greater is the sequence of different digits before repetition.

Note that a fraction consists of two co-prime numbers when it is cannot be reduced further (Eg: 2/4 can be reduced to 1/2; but 1/2 cannot be reduced further).
Here, all fractions are in their lowest form. Hence, all these fractions consist of two co-prime numbers each.

Since 37 is the largest denominator, it is the answer.
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Re: Which of the following fractions when expressed as repeating decimals [#permalink]
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Bunuel wrote:
Which of the following fractions when expressed as repeating decimals would have the longest sequence of different digits?

A. 2/11
B. 1/3
C. 41/99
D. 2/3
E. 23/37



The number of unique digits that are repeating in a repeating decimal depends on whether the denominator in its fractional equivalent is a factor of a number with all digits of 9 (i.e, 9, 99, 999, and so on). If it is a factor of 9 (in which 9 is the smallest number such that it is a factor), then it has 1 unique digit repeating. If it is a factor of 99 (in which 99 is the smallest number such that it is a factor), then it has 2 unique digits repeating. If it is a factor of 999 (in which 999 is the smallest number such that it is a factor), then it has 3 unique digits repeating.

For example, 3 is a factor of 9, so both 1/3 and 2/3, when expressed as a repeating decimal, have 1 unique digit repeating (notice that 1/3 = 0.333… and 2/3 = 0.666…). Similarly, since 11 and 99 are factors of 99, so both 2/11 and 41/99, when expressed as a repeating decimal, have 2 unique digits repeating (notice that 2/11 = 0.181818… and 41/99 = 0.414141…). Finally, 37 is neither a factor of 9 nor a factor of 99, 23/37, when expressed as a repeating decimal, must have more than 2 unique digits repeating.

Answer: E
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Re: Which of the following fractions when expressed as repeating decimals [#permalink]
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Utki01 wrote:
Trick: If a fraction consists of two co-prime numbers, then the larger the denominator, the greater is the sequence of different digits before repetition.


This is not true at all, as you can easily see by comparing the decimal expansion of 1/7 and of 1/9, say. The size of the denominator has very little to do with the length of the repeating pattern of digits. Scott has correctly explained the theory in the post above mine.
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If each of the following fractions were written as a repeati [#permalink]
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If each of the following fractions were written as a repeating decimal, which would have the longest sequence of different digits?

A) 2/11
B) 1/3
C) 41/99
D) 2/3
E) 23/37

We already know a few fraction to decimal equivalents.

1/3 = .33333
1/11 = .090909 (so 2/11 = .18181818...)
1/9 = .1111111
1/99 = .010101... (so 41/99 = .41414141...)

So two of the options have 1 repeating digit and two have 2 repeating digits.

Since there can be only 1 answer, answer must be the leftover option (E).
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Re: If each of the following fractions were written as a repeati [#permalink]
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gmatraider wrote:
If each of the following fractions were written as a repeating decimal, which would have the longest sequence of different digits?

A) 2/11
B) 1/3
C) 41/99
D) 2/3
E) 23/37


The number of digits in the decimal depends on the number of 9s in the denominator. For example:

5/9 = 0.555555... => single digit repeating
13/99 = 0.13131313.... => 2 digits repeating
137/999 = 0.137137137... => 3 digits repeating, and so on

A) 2/11 = 18/99 = 0.18181818... => 2 digits repeat
B) 1/3 = 3/9 = 0.3333... => 1 digit repeats
C) 41/99 = 0.414141... => 2 digits repeat
D) 2/3 = 6/9 = 0.6666... => 1 digit repeats
E) 23/37 = (23*3)/(37*3) = 69/111 = (69*9)/(111*9) = 621/999 = 0.621621621... => 3 digits repeat (the longest sequence)

Hence, the correct answer is E
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Re: If each of the following fractions were written as a repeati [#permalink]
Asked: If each of the following fractions were written as a repeating decimal, which would have the longest sequence of different digits?

A) 2/11 = 0.1818 : 2 different digits
B) 1/3 = 0.333 : 1 different digit
C) 41/99 = 0.3131 : 2 diffrent digits
D) 2/3 0.6666 : 1 different digit
E) 23/37 = 69/111 = 0.621621 : 3 different digits

IMO E
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Re: If each of the following fractions were written as a repeati [#permalink]
To determine which fraction would have the longest sequence of different digits when written as a repeating decimal, we need to convert each fraction into its decimal form.

A) 2/11:
To convert 2/11 into a decimal, we divide 2 by 11:
2 ÷ 11 = 0.181818...
The decimal representation of 2/11 is a repeating decimal with a sequence of 18.

B) 1/3:
To convert 1/3 into a decimal, we divide 1 by 3:
1 ÷ 3 = 0.333333...
The decimal representation of 1/3 is a repeating decimal with a sequence of 3.

C) 41/99:
To convert 41/99 into a decimal, we divide 41 by 99:
41 ÷ 99 = 0.414141...
The decimal representation of 41/99 is a repeating decimal with a sequence of 41.

D) 2/3:
To convert 2/3 into a decimal, we divide 2 by 3:
2 ÷ 3 = 0.666666...
The decimal representation of 2/3 is a repeating decimal with a sequence of 6.

E) 23/37:
To convert 23/37 into a decimal, we divide 23 by 37:
23 ÷ 37 ≈ 0.621621621...
The decimal representation of 23/37 is a repeating decimal with a sequence of 621.

From the given fractions, we can see that the fraction with the longest sequence of different digits when written as a repeating decimal is 23/37.

Therefore, the correct answer is (E) 23/37.
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Re: If each of the following fractions were written as a repeati [#permalink]
If denominator is 9, 99, 999 or any number equal to power of 10 minus 1, then numerator tell you the repeating digit. For example, 23÷99= 0.23232323...

(A) 2÷11= 18÷99= 0.181818......
(B) 1÷3= 3÷9= 0.3333.......
(C) 41÷99= 0.414141....
(D) 2÷3= 6÷9= 0.6666...
(E) 23÷37= 0.621621621....

Therefore, the answer is (E)
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