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Am I missing something?? (no calculator on this?)

This topic has 1 expert reply and 6 member replies
tzink Senior | Next Rank: 100 Posts Default Avatar
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Am I missing something?? (no calculator on this?)

Post Thu Jul 10, 2008 9:12 pm
The question is from the OG

If the units digit of integer n is greater than 2, what is the units digit of n?

1) The units digit of n is the same as the units digit of n^2

2) The units digit of n is the same as the units digit of n^3

The correct answer is E, but what I'm more worried about is the guide's explanation of how to arrive at the answer:

"To solve this problem, it is necessary to find a digit that is the same as the units digit of its square. For example, both 43 squared (1,849) and 303 squared (91,809) [why of course! i know all my squares up to a million by heart!] have a units digit of 9, which is different from the units digit of 43 and 303. However, 25 squared (625) and 385 squared (148,225) both have a units digit of 5, and 16 and 225 both have a units digit of 6 and their squares (256 and 51,076) do, too. There is no other information to choose between 5 or 6, so (1) is not sufficient."

Even worse, when explaining why the second statement is insufficient, they do the same thing with cubes! How on earth are we expected to do this without a calculator? and in two minutes?? unreal!

Are there shorter methods to this? just guess and move on?

cheers

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rajman41 Newbie | Next Rank: 10 Posts Default Avatar
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Post Wed Feb 10, 2010 10:43 pm
What's tat " E " for answers mean Error or 5=E( alphabet , a=1, b=2......).
5 satisfies both the requirement to be a solid answer. Why didn't they choose #5?

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sanju09 GMAT Instructor
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Post Wed Feb 10, 2010 11:33 pm
tzink wrote:
The question is from the OG

If the units digit of integer n is greater than 2, what is the units digit of n?

1) The units digit of n is the same as the units digit of n^2

2) The units digit of n is the same as the units digit of n^3

The correct answer is E, but what I'm more worried about is the guide's explanation of how to arrive at the answer:

"To solve this problem, it is necessary to find a digit that is the same as the units digit of its square. For example, both 43 squared (1,849) and 303 squared (91,809) [why of course! i know all my squares up to a million by heart!] have a units digit of 9, which is different from the units digit of 43 and 303. However, 25 squared (625) and 385 squared (148,225) both have a units digit of 5, and 16 and 225 both have a units digit of 6 and their squares (256 and 51,076) do, too. There is no other information to choose between 5 or 6, so (1) is not sufficient."

Even worse, when explaining why the second statement is insufficient, they do the same thing with cubes! How on earth are we expected to do this without a calculator? and in two minutes?? unreal!

Are there shorter methods to this? just guess and move on?

cheers
Sorry tzink, I was about to click “Quote” icon to write my reply but it slipped and clicked otherwise.

Besides, (1) is possible with unit’s digit 5 or 6 only. Insufficient

(2) This for a second time happens with unit’s digit 4, 5, 6, or 9. Insufficient

Taken together in turn leaves us with 5 or 6 to choose from. Insufficient

E

_________________
The mind is everything. What you think you become. –Lord Buddha



Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com

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rajman41 Newbie | Next Rank: 10 Posts Default Avatar
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Posted:
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Post Wed Feb 10, 2010 10:43 pm
What's tat " E " for answers mean Error or 5=E( alphabet , a=1, b=2......).
5 satisfies both the requirement to be a solid answer. Why didn't they choose #5?

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sanju09 GMAT Instructor
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Post Wed Feb 10, 2010 11:33 pm
tzink wrote:
The question is from the OG

If the units digit of integer n is greater than 2, what is the units digit of n?

1) The units digit of n is the same as the units digit of n^2

2) The units digit of n is the same as the units digit of n^3

The correct answer is E, but what I'm more worried about is the guide's explanation of how to arrive at the answer:

"To solve this problem, it is necessary to find a digit that is the same as the units digit of its square. For example, both 43 squared (1,849) and 303 squared (91,809) [why of course! i know all my squares up to a million by heart!] have a units digit of 9, which is different from the units digit of 43 and 303. However, 25 squared (625) and 385 squared (148,225) both have a units digit of 5, and 16 and 225 both have a units digit of 6 and their squares (256 and 51,076) do, too. There is no other information to choose between 5 or 6, so (1) is not sufficient."

Even worse, when explaining why the second statement is insufficient, they do the same thing with cubes! How on earth are we expected to do this without a calculator? and in two minutes?? unreal!

Are there shorter methods to this? just guess and move on?

cheers
Sorry tzink, I was about to click “Quote” icon to write my reply but it slipped and clicked otherwise.

Besides, (1) is possible with unit’s digit 5 or 6 only. Insufficient

(2) This for a second time happens with unit’s digit 4, 5, 6, or 9. Insufficient

Taken together in turn leaves us with 5 or 6 to choose from. Insufficient

E

_________________
The mind is everything. What you think you become. –Lord Buddha



Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com

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bynddrvn Senior | Next Rank: 100 Posts Default Avatar
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Post Sat Sep 20, 2014 7:05 am
The creators of the test assume you will be able to figure out shortcuts.

Although, I must confess I do not understand why the test makers insist on sticking to solving mathematical problems with a stylus and tablet when the rest of the civilized world uses calculators or spreadsheets. Heck, I know welders and plumbers who use spreadsheets and most MBA programs require you bring a laptop to class.

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cubicle_bound_misfit Master | Next Rank: 500 Posts
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Post Fri Jul 11, 2008 8:07 am
There are more things in heaven and earth, TZINK
Than are taught by OG.

That's why let's beat the s_ out of GMAT.



Regards,

_________________
Cubicle Bound Misfit

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tzink Senior | Next Rank: 100 Posts Default Avatar
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Post Fri Jul 11, 2008 7:58 am
yeah, that makes it much more manageable..
why wouldn't the OG tell me that?

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