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Any decimal that has only a finite number of nonzero digits [#permalink]
30 Sep 2010, 03:28

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C

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Difficulty:

35% (medium)

Question Stats:

54% (01:50) correct
46% (00:43) wrong based on 240 sessions

Any decimal that has only a finite number of nonzero digits is a terminating decimal. For example, 12, 0.13, and 4.068 are three terminating decimals. If j and k are positive integers and the ratio j/k is expressed as a decimal, is j/k a terminating decimal?

Reduced fraction \frac{a}{b} (meaning that fraction is already reduced to its lowest term) can be expressed as terminating decimal if and onlyb (denominator) is of the form 2^n5^m, where m and n are non-negative integers. For example: \frac{7}{250} is a terminating decimal 0.028, as 250 (denominator) equals to 2*5^3. Fraction \frac{3}{30} is also a terminating decimal, as \frac{3}{30}=\frac{1}{10} and denominator 10=2*5.

Note that if denominator already has only 2-s and/or 5-s then it doesn't matter whether the fraction is reduced or not.

For example \frac{x}{2^n5^m}, (where x, n and m are integers) will always be terminating decimal.

(We need reducing in case when we have the prime in denominator other then 2 or 5 to see whether it could be reduced. For example fraction \frac{6}{15} has 3 as prime in denominator and we need to know if it can be reduced.)

BACK TO THE ORIGINAL QUESTION: Any decimal that has only a finite number of nonzero digits is a terminating decimal. For example, 12, 0.13, and 4.068 are three terminating decimals. If j and k are positive integers and the ratio j/k is expressed as a decimal, is j/k a terminating decimal?

(1) k = 3 --> now, if j=3p (j is a multiple of 3) then \frac{j}{k}=\frac{3p}{3}=p=integer=terminating \ decimal but if j is not a multiple of 3 then reduced fraction \frac{j}{k}=\frac{j}{3} won't be a terminating decimal, as denominator has primes other than 2 and/or 5. Not sufficient.

(2) j is an odd multiple of 3 --> j=3(2k+1), clearly insufficient as no info about the denominator k.

Re: Terminating Decimal [#permalink]
07 Oct 2010, 00:19

But it says the ratio j/k is expressed as a decimal, so how come j=3p ? I thought answer is A since J has to be a non-multiple of 3 since if it is a multiple of 3, j/k cannot be expressed as a decimal. COrrect me if i am wrong!

Re: Terminating Decimal [#permalink]
07 Oct 2010, 00:36

psychomath wrote:

But it says the ratio j/k is expressed as a decimal, so how come j=3p ? I thought answer is A since J has to be a non-multiple of 3 since if it is a multiple of 3, j/k cannot be expressed as a decimal. COrrect me if i am wrong!

Anser can't be A. Because just knowing that k=3, doesnt tell you much about the decimal. For instance if j and k do not have 3 as a common factor, it will not cancel out and you will not get a terminating decimal which you would if they do have 3 as a common factor.

Eg. j=1, k=3 : Decimal is 0.333333.... j=6, k=3 : Decimal is 2.0 _________________

Re: Terminating Decimal [#permalink]
08 Oct 2010, 10:08

psychomath wrote:

But it says the ratio j/k is expressed as a decimal, so how come j=3p ? I thought answer is A since J has to be a non-multiple of 3 since if it is a multiple of 3, j/k cannot be expressed as a decimal. COrrect me if i am wrong!

Can;t be true.. j can be a multiple of 3. _________________

GGG (Gym / GMAT / Girl) -- Be Serious

Its your duty to post OA afterwards; some one must be waiting for that...

Re: Terminating Decimal [#permalink]
17 Oct 2013, 04:49

Bunuel wrote:

THEORY:

Reduced fraction \frac{a}{b} (meaning that fraction is already reduced to its lowest term) can be expressed as terminating decimal if and onlyb (denominator) is of the form 2^n5^m, where m and n are non-negative integers. For example: \frac{7}{250} is a terminating decimal 0.028, as 250 (denominator) equals to 2*5^3. Fraction \frac{3}{30} is also a terminating decimal, as \frac{3}{30}=\frac{1}{10} and denominator 10=2*5.

Note that if denominator already has only 2-s and/or 5-s then it doesn't matter whether the fraction is reduced or not.

For example \frac{x}{2^n5^m}, (where x, n and m are integers) will always be terminating decimal.

(We need reducing in case when we have the prime in denominator other then 2 or 5 to see whether it could be reduced. For example fraction \frac{6}{15} has 3 as prime in denominator and we need to know if it can be reduced.)

BACK TO THE ORIGINAL QUESTION: Any decimal that has only a finite number of nonzero digits is a terminating decimal. For example, 12, 0.13, and 4.068 are three terminating decimals. If j and k are positive integers and the ratio j/k is expressed as a decimal, is j/k a terminating decimal?

(1) k = 3 --> now, if j=3p (j is a multiple of 3) then \frac{j}{k}=\frac{3p}{3}=p=integer=terminating \ decimal but if j is not a multiple of 3 then reduced fraction \frac{j}{k}=\frac{j}{3} won't be a terminating decimal, as denominator has primes other than 2 and/or 5. Not sufficient.

(2) j is an odd multiple of 3 --> j=3(2k+1), clearly insufficient as no info about the denominator k.

Re: Terminating Decimal [#permalink]
17 Oct 2013, 07:39

Expert's post

jlgdr wrote:

Bunuel wrote:

THEORY:

Reduced fraction \frac{a}{b} (meaning that fraction is already reduced to its lowest term) can be expressed as terminating decimal if and onlyb (denominator) is of the form 2^n5^m, where m and n are non-negative integers. For example: \frac{7}{250} is a terminating decimal 0.028, as 250 (denominator) equals to 2*5^3. Fraction \frac{3}{30} is also a terminating decimal, as \frac{3}{30}=\frac{1}{10} and denominator 10=2*5.

Note that if denominator already has only 2-s and/or 5-s then it doesn't matter whether the fraction is reduced or not.

For example \frac{x}{2^n5^m}, (where x, n and m are integers) will always be terminating decimal.

(We need reducing in case when we have the prime in denominator other then 2 or 5 to see whether it could be reduced. For example fraction \frac{6}{15} has 3 as prime in denominator and we need to know if it can be reduced.)

BACK TO THE ORIGINAL QUESTION: Any decimal that has only a finite number of nonzero digits is a terminating decimal. For example, 12, 0.13, and 4.068 are three terminating decimals. If j and k are positive integers and the ratio j/k is expressed as a decimal, is j/k a terminating decimal?

(1) k = 3 --> now, if j=3p (j is a multiple of 3) then \frac{j}{k}=\frac{3p}{3}=p=integer=terminating \ decimal but if j is not a multiple of 3 then reduced fraction \frac{j}{k}=\frac{j}{3} won't be a terminating decimal, as denominator has primes other than 2 and/or 5. Not sufficient.

(2) j is an odd multiple of 3 --> j=3(2k+1), clearly insufficient as no info about the denominator k.

Re: Any decimal that has only a finite number of nonzero digits [#permalink]
25 Oct 2013, 12:36

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This is a GMAT Hacks question of the day. The question reappeared on May 8, 2013. Here is the official explanation in case anyone was interested.

Answer: C Statement (1) is insufficient. If the denominator of the fraction is 3, the decimal would be terminating if the numerator is a multiple of 3. For instance, 6/3 = 2, a terminating decimal. However, if the numerator is not a multiple of 3, it will not be terminating, as in 7/3 = 2.33.

Statement (2) is also insufficient. The important factor in determining whether a fraction is equivalent to a terminating decimal is the denominator. If j = 9, the fraction could be 9/3 (terminating) or 9/7 (not terminating).

Taken together, the statements are sufficient. j/k is equal to (3(integer))/3 = integer. An integer is, as defined in the question itself, a terminating decimal. Choice (C) is correct.