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

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

by tzink » Thu Jul 10, 2008 9:12 pm

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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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Source: — Data Sufficiency |
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by louvre » Fri Jul 11, 2008 7:07 am

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From 1. Only those numbers with 5 and 0 in their unit's place satisfy the given condition. But we can't pin on one of the two possibilities.

From 2. It filters to the same possibilities of 5 and 0.

So none of the 2 clues is sufficient.
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by cubicle_bound_misfit » Fri Jul 11, 2008 7:37 am

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Leran the cyclicity for finding unit digits.

2 has a cyclicity of 4

i.e 2 sqare unit dig :4
2 cube unit digit : 8
2 to the power four unit digit : 6

so, cyclicity 2-4-8-6 then repeat from 2^5

similarly 3

3-9-7-1

for 4
4-6-

for 5
5-
for 6
6

for 7
7 -9-3-1
for 8
8-4-2-6
for 9
9-1

So you can easily see for both the conditions 5 and 6 will have cube and squares unit digit same.

Hope this will help.

regards,
Cubicle Bound Misfit
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by tzink » Fri Jul 11, 2008 7:58 am

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yeah, that makes it much more manageable..
why wouldn't the OG tell me that?
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by cubicle_bound_misfit » Fri Jul 11, 2008 8:07 am

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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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by rajman41 » Wed Feb 10, 2010 10:43 pm

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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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by sanju09 » Wed Feb 10, 2010 11:33 pm

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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

[spoiler]E[/spoiler]
The mind is everything. What you think you become. -Lord Buddha



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

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by bynddrvn » Sat Sep 20, 2014 7:05 am

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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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by [email protected] » Fri Feb 16, 2018 4:25 pm

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Hi All,

We're told that the units digit of integer N is greater than 2. We're asked for the units digit of N. This question can be solved with a bit of Arithmetic and some Number Property patterns. Since all of the given information (including what's in the two Facts) relates to units digits, I'm going to list out the values from 3-9:

N, N^2, N^3
3, 9, 27
4, 16, 64
5, 25, 125
6, 36, 216
7, 49, 343
8, 64, 512
9, 81, 729

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

Based on the information in Fact 1, the units digit of N could be 5 or 6.
Fact 1 is INSUFFICIENT

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

Based on the information in Fact 2, the units digit of N could be 5 or 6.
Fact 2 is INSUFFICIENT

Combined, we already have 2 values that 'fit' both Facts.
Combined, INSUFFICIENT

Final Answer: E

GMAT assassins aren't born, they're made,
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Contact Rich at [email protected]
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by Jeff@TargetTestPrep » Fri May 18, 2018 10:35 am

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tzink wrote:
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
We are given that the units digit of integer n is greater than 2 and we need to determine that units digit.

Statement One Alone:

The units digit of n is the same as the units digit of n^2.

If the units digit of n is the same as the units digit of n^2, then the units digit can be 0, 1, 5, or 6 (since 0^2 = 0, 1^2 = 1, 5^2 = 25 and 6^2 = 36). However, we are given that the units digits is greater than 2, so n can be either 5 or 6. Since we can't determine exactly which digit it is, statement one alone is not sufficient to answer the question.

Statement Two Alone:

The units digit of n is the same as the units digit of n^3.

If the units digit of n is the same as the units digit of n^2, then the units digit can be 0, 1, 4, 5, 6, or 9. (since 0^3 = 0, 1^3 = 1, 4^3 = 64, 5^3 = 125, 6^3 = 216 and 9^3 = 729). However, we are given that the units digits is greater than 2, so n can be 4, 5, 6 or 9. Since we can't determine exactly which digit it is, statement two alone is not sufficient to answer the question.

Statements One and Two Together:

With two statements together, the units digit of n can still be either 5 or 6. Since we can't determine which one it is, the two statements together are still not sufficient to answer the question.

Answer: E

Jeffrey Miller
Head of GMAT Instruction
[email protected]

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