GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 17 Feb 2019, 21:22

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

## Events & Promotions

###### Events & Promotions in February
PrevNext
SuMoTuWeThFrSa
272829303112
3456789
10111213141516
17181920212223
242526272812
Open Detailed Calendar
• ### Free GMAT Algebra Webinar

February 17, 2019

February 17, 2019

07:00 AM PST

09:00 AM PST

Attend this Free Algebra Webinar and learn how to master Inequalities and Absolute Value problems on GMAT.
• ### Valentine's day SALE is on! 25% off.

February 18, 2019

February 18, 2019

10:00 PM PST

11:00 PM PST

We don’t care what your relationship status this year - we love you just the way you are. AND we want you to crush the GMAT!

# Which of the following is a perfect square?

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 52906
Which of the following is a perfect square?  [#permalink]

### Show Tags

28 Feb 2016, 07:16
00:00

Difficulty:

45% (medium)

Question Stats:

60% (01:33) correct 40% (01:20) wrong based on 232 sessions

### HideShow timer Statistics

Which of the following is a perfect square?

A. 649
B. 961
C. 1664
D. 2509
E. 100000

_________________
Math Expert
Joined: 02 Aug 2009
Posts: 7334
Which of the following is a perfect square?  [#permalink]

### Show Tags

28 Feb 2016, 08:43
5
4
Bunuel wrote:
Which of the following is a perfect square?

A. 649
B. 961
C. 1664
D. 2509
E. 100000

Hi,
Normally you will start checking by division method..
But the choices should stand out, as they seem to be combination of perfect square..
649--64 and 9 are perfect square
1664---16 and 64 are perfect square
2509--- 25 and 09 are perfect square

The best way would be to see the range in tens and solve after looking at the units digit
lets see all choices--
A. 649
$$20^2=400$$ and $$30^2=900$$..
since only 3 and 7 have the perfect square ending in 9, we require to try only for 27 as it is more than 25^2, 625
it is not $$27^2$$, as next square of 26 itself after 625 will be $$>625+2*25$$ or $$>675$$
actually $$26^2$$ will be $$25^2+25+26$$

B. 961
between 30^2 and 40^2...
only 1 and 9 have squares ending with onw..
since it is very close to 30^2, 900.. it can be 31^2
CORRECT

C. 1664
between 40^2 and 50^2..
closer is 42, but that should be atleast 1600+41+42.. NO

D. 2509
between 50^2 and 60^2..
very close to 50^2 so next square of 51 will be atleast 2500+51.. no

E. 100000
odd number of 0s, not possible

ans B
_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html
4) Base while finding % increase and % decrease : https://gmatclub.com/forum/percentage-increase-decrease-what-should-be-the-denominator-287528.html

GMAT Expert

##### General Discussion
Intern
Joined: 06 Oct 2013
Posts: 45
Re: Which of the following is a perfect square?  [#permalink]

### Show Tags

07 Mar 2016, 12:53
2
Bunuel wrote:
Which of the following is a perfect square?

A. 649
B. 961
C. 1664
D. 2509
E. 100000

Solution.

Two important things before solving the problem to make easy.

--> First, look at the units digit in every option, For example. 1) 649--> you can get 9 as a unit digit by squaring the digit 3 or 7.

2) 961---> you can get 1 as a unit digit by squaring the digit 1 or 9.

-->Second, we know squares of 10,20,30,40,50 ,60... and Formula $$(a+b)^2=a^2+2ab+b^2$$

Now for Option A).649--> We know (20)^2=400, and (30)^2=900. So the digit should be between 20 and 30. try (20+3)^2 or (20+7)^2.

$$(20+3)^2=400+120+9=529--No$$
$$(20+7)^2=400+280+49=729--No$$

Option B).961--> we know that (30)^2=900, $$(30+1)^2=900+60+1=961--->YES$$

try all remaining--$$(30+9)^2=900+540+81=1521--->NO$$

Option C).1664
--> we know that (40)^2=1600, $$(40+2)^2=1600+160+4=1764-->NO$$

$$(40+8)^2=1600+640+64=2304---> NO.$$

Option D) 2509-->. We know that (50)^2=2500, $$(50+3)^2=2500+300+9=2809--> NO$$

$$(50+7)^2=2500+700+49=3249--> NO$$

E) No need to check as it has odd number of 0'-->no.

Ans.B
Non-Human User
Joined: 09 Sep 2013
Posts: 9838
Re: Which of the following is a perfect square?  [#permalink]

### Show Tags

10 Oct 2018, 04:35
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Re: Which of the following is a perfect square?   [#permalink] 10 Oct 2018, 04:35
Display posts from previous: Sort by