What arithmetic should I memorize? : GMAT Quantitative Section
Check GMAT Club App Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 08 Dec 2016, 00:40

### 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 June
Open Detailed Calendar

# What arithmetic should I memorize?

Author Message
TAGS:

### Hide Tags

Senior Manager
Joined: 25 Mar 2009
Posts: 305
Followers: 7

Kudos [?]: 204 [16] , given: 6

What arithmetic should I memorize? [#permalink]

### Show Tags

25 Jun 2009, 20:39
16
KUDOS
134
This post was
BOOKMARKED
I find myself constantly using long division and multiplication for simple things like 13 x 11.

What are some good arithmetic calcs to memorize? I created a 20x20 multiplication table but this seems like a bit much right?

Perfect squares up to 100? $$\sqrt{3}$$? $$\sqrt{5}$$?

I am not really talking about formulas to memorize since you should definitely memorize things like nCr, nPr, sum of all #'s in an evenly spaced set, etc.
Founder
Affiliations: AS - Gold, HH-Diamond
Joined: 04 Dec 2002
Posts: 14235
Location: United States (WA)
GMAT 1: 750 Q49 V42
GPA: 3.5
Followers: 3652

Kudos [?]: 22434 [63] , given: 4450

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

25 Jun 2009, 21:18
63
KUDOS
Expert's post
56
This post was
BOOKMARKED
Fantastic question

This file should give you an idea where you are lacking.
I think you should definitely know the squares from 0-10 and preferrably from 10 to 20 as well.
Attachments

Arithmetic Fractions and Percentages.doc [32.5 KiB]

_________________

Founder of GMAT Club

US News Rankings progression - last 10 years in a snapshot - New!
Just starting out with GMAT? Start here...
Need GMAT Book Recommendations? Best GMAT Books

Co-author of the GMAT Club tests

GMAT Club Premium Membership - big benefits and savings

Senior Manager
Joined: 25 Mar 2009
Posts: 305
Followers: 7

Kudos [?]: 204 [0], given: 6

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

26 Jun 2009, 10:19
Thank you bb. I think I will just try to squeeze in as much as I can until test time.
Intern
Joined: 10 Sep 2009
Posts: 27
Followers: 0

Kudos [?]: 33 [0], given: 10

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

10 Sep 2009, 12:53
Very gud doc....it will be helful for anyone who's taking GMAT...
Manager
Joined: 12 May 2009
Posts: 54
Followers: 2

Kudos [?]: 93 [50] , given: 18

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

21 Oct 2009, 23:59
50
KUDOS
38
This post was
BOOKMARKED
As far as common squares are concerned, I only remember the ones with 0 or 5 in the units digit. For the latter category, I use the following process:

For example: 65*65

1) Always write down 25 as this is always the last two digits of the result:
...25

2) Multiply (non-units digits) times (non-units digits + 1)
6 * (6+1) = 42

2c) Combine:
4225

This way I always have the important squares handy... very useful for estimations!

Any other math shortcuts? Anyone

Steve
Manager
Joined: 05 Jul 2009
Posts: 182
Followers: 1

Kudos [?]: 46 [1] , given: 5

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

23 Oct 2009, 21:04
1
KUDOS
1
This post was
BOOKMARKED
@bb: Thanks
@enfinity: good technique but I guess one need time to get familiar and comfortable with it. Up to then the conventional way is better.
Manager
Joined: 12 May 2009
Posts: 54
Followers: 2

Kudos [?]: 93 [0], given: 18

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

24 Oct 2009, 02:33
@eresh: what's the conventional way? memorizing?
Manager
Joined: 05 Jul 2009
Posts: 182
Followers: 1

Kudos [?]: 46 [0], given: 5

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

24 Oct 2009, 20:25
enfinity wrote:
@eresh: what's the conventional way? memorizing?

Well...god have not gave me such kind of superbrain....I was taking about simple multiplication The one we were taught on schools....
Intern
Joined: 24 Oct 2009
Posts: 24
Location: Russia
Schools: IESE, SDA Bocconi
Followers: 1

Kudos [?]: 85 [48] , given: 4

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

31 Oct 2009, 08:56
48
KUDOS
34
This post was
BOOKMARKED
I'm new here, and try to go through all the topics - this site is a treasure!

Maybe not the right place to share my experience with "multiplication for simple things like 13 x 11", but anyway...if you need to multiply any two-digits number by 11, just sum those digits and put the result in between. For example,
13x11 -> 1+3=4 -> 143 is the result.
Or, 36x11 -> 3+6=9 -> the result is 36x11=396.

It really saves time.
Intern
Joined: 31 Oct 2009
Posts: 38
Followers: 1

Kudos [?]: 49 [23] , given: 0

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

31 Oct 2009, 19:21
23
KUDOS
17
This post was
BOOKMARKED
Shelen wrote:
I'm new here, and try to go through all the topics - this site is a treasure!

Maybe not the right place to share my experience with "multiplication for simple things like 13 x 11", but anyway...if you need to multiply any two-digits number by 11, just sum those digits and put the result in between. For example,
13x11 -> 1+3=4 -> 143 is the result.
Or, 36x11 -> 3+6=9 -> the result is 36x11=396.

It really saves time.

And if it equals more than 10, add a 1 to the first digit

EG

68*11 -> 6+8=14 -> 6 14 8 -> 748
Intern
Joined: 26 Oct 2009
Posts: 2
Followers: 0

Kudos [?]: 0 [0], given: 1

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

01 Nov 2009, 12:40
bb - Many thanks, this is very helpful.
Manager
Joined: 05 Jul 2009
Posts: 182
Followers: 1

Kudos [?]: 46 [0], given: 5

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

03 Nov 2009, 00:28
Indeed very helpful. Thanks a lot.
Manager
Joined: 22 Sep 2009
Posts: 222
Location: Tokyo, Japan
Followers: 2

Kudos [?]: 22 [1] , given: 8

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

18 Nov 2009, 20:28
1
KUDOS
Good document. Should bump this up for ppl to download and memorize
Intern
Joined: 12 Oct 2009
Posts: 30
Location: I see you
Followers: 0

Kudos [?]: 5 [0], given: 1

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

07 Jan 2010, 13:26
Thanks specially the 11 multiplication helps
_________________

Be willing to fail. It's the price of greatness.

Founder
Affiliations: AS - Gold, HH-Diamond
Joined: 04 Dec 2002
Posts: 14235
Location: United States (WA)
GMAT 1: 750 Q49 V42
GPA: 3.5
Followers: 3652

Kudos [?]: 22434 [1] , given: 4450

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

07 Jan 2010, 16:13
1
KUDOS
Expert's post
3
This post was
BOOKMARKED
Also, see this post for some good theory: math-number-theory-88376.html
_________________

Founder of GMAT Club

US News Rankings progression - last 10 years in a snapshot - New!
Just starting out with GMAT? Start here...
Need GMAT Book Recommendations? Best GMAT Books

Co-author of the GMAT Club tests

GMAT Club Premium Membership - big benefits and savings

Manager
Joined: 24 Jul 2009
Posts: 193
Location: Anchorage, AK
Schools: Mellon, USC, MIT, UCLA, NSCU
Followers: 4

Kudos [?]: 36 [1] , given: 10

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

09 Jan 2010, 19:05
1
KUDOS
Shelen wrote:
I'm new here, and try to go through all the topics - this site is a treasure!

Maybe not the right place to share my experience with "multiplication for simple things like 13 x 11", but anyway...if you need to multiply any two-digits number by 11, just sum those digits and put the result in between. For example,
13x11 -> 1+3=4 -> 143 is the result.
Or, 36x11 -> 3+6=9 -> the result is 36x11=396.

Thanks for the tips. I recently downloaded some math apps to learn shortcuts. I plan to use them minimially though given the geometry and other formulas I need to memorize.
It really saves time.

Posted from my mobile device
_________________

Reward wisdom with kudos.

Senior Manager
Status: Not afraid of failures, disappointments, and falls.
Joined: 20 Jan 2010
Posts: 294
Concentration: Technology, Entrepreneurship
WE: Operations (Telecommunications)
Followers: 17

Kudos [?]: 225 [35] , given: 260

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

11 Feb 2010, 09:34
35
KUDOS
19
This post was
BOOKMARKED
Thanks for sharing the Doc bb...@Shelen & @jeckll...Thanks for the tip but I would like to add some more.

What if u need to multiply 3 digits or 4 didgits by 11...the procedure is same as u mentioned but it would be done like below

For 3 digits
133x11 --> 1 1+3 3+3 3=1463
And for 4 digits
1243x11 --> 1 1+2 2+4 4+3 3=13673

And for 5 digits
15453x11 --> 1 1+5 5+4 4+5 5+3 3=169983
and so on.
you can plug other numbers in and check it out.

Hope it helps!
_________________

"I choose to rise after every fall"
Target=770
http://challengemba.blogspot.com
Kudos??

Senior Manager
Status: Not afraid of failures, disappointments, and falls.
Joined: 20 Jan 2010
Posts: 294
Concentration: Technology, Entrepreneurship
WE: Operations (Telecommunications)
Followers: 17

Kudos [?]: 225 [11] , given: 260

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

11 Feb 2010, 21:41
11
KUDOS
17
This post was
BOOKMARKED
Guys! I just found another way of checking whether a number is divisible by 8 or not ( the rule is same but another approach or route ). It's for a number with more than two digits.

Let's take 1936
1) First of all check whether last two digits of the number are divisible by 4 or not.
For 1936, we do this way 36/4=9

2) If it is divisible by 4 then add the quotient to the 3rd last digit of the number and if the sum of them is divisible by 2 then the whole number is divisible by 8.

--> 9 (quotient)+ 9 ( 3rd digit from right)= 18, and -->18/2=9
So the whole number is divisible by 8.

Once you understand it and do a little practice, you'll find it easy and fast.
**You can try other numbers to see whether it is true or not
Hope it helps!
_________________

"I choose to rise after every fall"
Target=770
http://challengemba.blogspot.com
Kudos??

Intern
Affiliations: isa.org
Joined: 26 Jan 2010
Posts: 23
Location: Mumbai, India.
Schools: ISB, India.
Followers: 0

Kudos [?]: 10 [3] , given: 2

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

14 Feb 2010, 05:12
3
KUDOS
2
This post was
BOOKMARKED
AtifS wrote:
Thanks for sharing the Doc bb...@Shelen & @jeckll...Thanks for the tip but I would like to add some more.

What if u need to multiply 3 digits or 4 didgits by 11...the procedure is same as u mentioned but it would be done like below

For 3 digits
133x11 --> 1 1+3 3+3 3=1463
And for 4 digits
1243x11 --> 1 1+2 2+4 4+3 3=13673

And for 5 digits
15453x11 --> 1 1+5 5+4 4+5 5+3 3=169983
and so on.
you can plug other numbers in and check it out.

Hope it helps!

welldone dude,
just a small addition which i tried and will help to avoid confusion:

start writing the answer from right hand side in case if the addition of two no. exceeds 10, and add it to consecutive no. on left hand side. try out!!
_________________

"Great people don't do different things, they do things differently"

Intern
Affiliations: isa.org
Joined: 26 Jan 2010
Posts: 23
Location: Mumbai, India.
Schools: ISB, India.
Followers: 0

Kudos [?]: 10 [3] , given: 2

Re: What arithmetic should I memorize? [#permalink]

### Show Tags

14 Feb 2010, 05:21
3
KUDOS
3
This post was
BOOKMARKED
AtifS wrote:
Guys! I just found another way of checking whether a number is divisible by 8 or not ( the rule is same but another approach or route ). It's for a number with more than two digits.

Let's take 1936
1) First of all check whether last two digits of the number are divisible by 4 or not.
For 1936, we do this way 36/4=9

2) If it is divisible by 4 then add the quotient to the 3rd last digit of the number and if the sum of them is divisible by 2 then the whole number is divisible by 8.

--> 9 (quotient)+ 9 ( 3rd digit from right)= 18, and -->18/2=9
So the whole number is divisible by 8.

Once you understand it and do a little practice, you'll find it easy and fast.
**You can try other numbers to see whether it is true or not
Hope it helps!

hi,
i feel the process is bit complicated as it doesn't give the value of quotient, it just tells you whether no. is divisible by 8.
here is another tric, if the no. formed by last three digits is divisible by 8 then the whole no. is divisible by 8.

953360 is divisible by 8 since 360 is divisible by 8,
529418: not divisible as 418 is not divisible by 8.

plug in different values and try.
_________________

"Great people don't do different things, they do things differently"

Re: What arithmetic should I memorize?   [#permalink] 14 Feb 2010, 05:21

Go to page    1   2   3   4    Next  [ 63 posts ]

Similar topics Replies Last post
Similar
Topics:
What to memorize for Quant (decimal equivalence, number properties,?) 1 29 Dec 2015, 22:47
69 What to Memorize in GMAT Quant for the GMAT 9 11 Jul 2013, 06:22
2 Am I supposed to memorize SQRTs? 3 31 May 2012, 12:46
Memorization? 3 20 Jan 2011, 11:59
3 What math formulas, items, etc. should be memorized 2 15 Aug 2009, 15:34
Display posts from previous: Sort by