Digits

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vinay1983: Legendary Member; Posts: 643; Joined: Wed Aug 14, 2013 4:27 amFollowed by: 7 members; Thanked: 48 times

by vinay1983 » Tue Aug 27, 2013 4:58 am

If d= 1/(2^3)*(5^7) is expressed as terminating decimal, how many non zero digits will d have?

A. 1
B. 2
C. 3
D. 7
E. 10

OA: B

OG 13, Digits. Also what is the frequency of such concepts or questions being tested on the GMAT?.

You can, for example never foretell what any one man will do, but you can say with precision what an average number will be up to!

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Source: Beat The GMAT — Problem Solving | Tue Aug 27, 2013 4:58 am

ganeshrkamath: Master | Next Rank: 500 Posts; Posts: 283; Joined: Sun Jun 23, 2013 11:56 pmFollowed by: 26 members; Location: Bangalore, India; Thanked: 97 times; GMAT Score:750

by ganeshrkamath » Tue Aug 27, 2013 6:10 am

vinay1983 wrote:If d= 1/(2^3)*(5^7) is expressed as terminating decimal, how many non zero digits will d have?

A. 1
B. 2
C. 3
D. 7
E. 10

OA: B

OG 13, Digits. Also what is the frequency of such concepts or questions being tested on the GMAT?.

d = 1/(2^3*5^7)
= 2^4/(2^7*5^7)
= 2^4/10^7
= 16/10^7
= 0.00...016

Total number of non-zero digits = 2

Choose B

To answer your question, it's difficult to put a number on the frequency of any concept in quant. All I can say is that it will depend on the difficulty levels of the questions you've solved till that point in time. The higher difficulty levels will try to give a question that requires multiple concepts or a concept not frequently used (for example, the number of factors of a number).
The above question looks like a medium-tough difficulty question.

Cheers

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Kelley School of Business (Class of 2016)
GMAT Score: 750 V40 Q51 AWA 5 IR 8
https://www.beatthegmat.com/first-attemp ... tml#688494

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GMAT/MBA Expert

[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

by [email protected] » Tue Aug 27, 2013 11:31 am

Hi vinay1983,

The concept of "digits" usually shows up 1-2 times on the GMAT, but it's not necessarily going to look like this question. While this question looks "scary", the truth is that it was designed (like most GMAT questions) to have a pattern-matching shortcut built in. Here, you'll notice all of the "zeros" that can be formed by multiplying a 2 by a 5. You can find many of the shortcuts if you try; by "try", I mean do work on the PAD, NOT by staring at the screen.

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

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