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Digits

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?.
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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.

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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.

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