I didn't even understand the question!

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rrobiinn: Junior | Next Rank: 30 Posts; Posts: 24; Joined: Tue Mar 06, 2012 5:35 am

by rrobiinn » Tue Jun 05, 2012 5:56 am

The question is for beyond my intuition. Need help. Please break it down as small parts as possible.

Which of the following fractions will terminate when expressed as a decimal?(Choose all
that apply.)

(A) 1/246
(B) 27/100
(C) 100/27
(D) 231/660
(E) 7/105

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Source: Beat The GMAT — Problem Solving | Tue Jun 05, 2012 5:56 am

1947: Master | Next Rank: 500 Posts; Posts: 215; Joined: Sat Jun 14, 2008 4:24 pmFollowed by: 1 member; Thanked: 13 times

by 1947 » Tue Jun 05, 2012 7:29 am

rrobiinn wrote:The question is for beyond my intuition. Need help. Please break it down as small parts as possible.

Which of the following fractions will terminate when expressed as a decimal?(Choose all
that apply.)

(A) 1/246
(B) 27/100
(C) 100/27
(D) 231/660
(E) 7/105

Reduce the fraction to smallest term...and if then in denominator you have only 2s and 5s..then that fraction will be terminating decimal.

A. will have 3 in dr.
B. only 2 and 5
C. 3 in dr.
D. reduces to 7/20 so only 2 and 5
E. 3 and 5 in dr.
so B and D

If my post helped you- let me know by pushing the thanks button. Thanks

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

by Stuart@KaplanGMAT » Tue Jun 05, 2012 10:34 am

rrobiinn wrote:The question is for beyond my intuition. Need help. Please break it down as small parts as possible.

Which of the following fractions will terminate when expressed as a decimal?(Choose all
that apply.)

(A) 1/246
(B) 27/100
(C) 100/27
(D) 231/660
(E) 7/105

Hi!

A terminating decimal is one that ends, i.e. doesn't infinitely repeat.

For example, 1.4, 8, 32.888991 and 27.6 are all terminating decimals.

Some fractions can be turned into terminating decimals, some can't. For example, 1/3 is .33333 (going on forever). 1/5 is .2, which is terminating.

As 1947 aptly notes, the rule for when a decimal will terminate is simple:

if the denominator of the reduced fraction can be expressed as a product of only 2s and 5s, then the decimal will terminate; if the denominator has any other primes in its factorization, then it will not terminate.

So, to answer the question you reduce the fraction in each choice as much as possible and then check the remaining denominators. An aggressive scan should very quickly point you to choice (B), which of course can be written as .27, a terminating decimal.

Now, this isn't a real GMAT question (there's no "choose all that apply"), so I'm guessing that it comes from a math textbook or the GRE (which has multiple answer questions). On the GMAT we'd just stop with B, but if we need to check all the choices:

A) 2+4+6=12, so 246 is a multiple of 3.. NOT terminating.

C) 27 is a multiple of 3.. NOT terminating. (can't reduce this fraction)

D) 231 and 660 are both multiples of 3, so reduce to 77/220.
77 and 220 are both multiples of 11, so reduce to 7/20.
No further reduction possible!
20 = 2*2*5... only 2s and 5s, so 7/20 IS terminating.

E) 7/105 = 1/15. 15 is a multiple of 3... NOT terminating.

Choose (B) and (D)!

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Tue Jun 05, 2012 7:46 pm

Refer to the post made by Rahul here >> https://www.beatthegmat.com/recurring-de ... tml#322950

The question is not identical, bu the concept is.

Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

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