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# What to Memorize in GMAT Quant for the GMAT

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What to Memorize in GMAT Quant for the GMAT [#permalink]  11 Jul 2013, 06:22
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What to Memorize in GMAT Quant for the GMAT

There are a few things you can memorize for GMAT Quant that will help you answer questions faster, minimize mistakes, and fill in any gaps and holes.
This post collects the best tips from GMAT Club with special credit going to einstein10.

Attachment:
Arithmetic Fractions and Percentages.pdf [64.34 KiB]

Attachment:
what_to_remember_gmat_Q.pdf [1.05 MiB]

Also some fun rules for not memorizing:

Multiples of 11
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.
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

For Multiples of 25
Multiplying 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
3) Combine:
4225

Have your own? Share them here!
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Last edited by bb on 17 Jul 2013, 07:10, edited 8 times in total.
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Re: What to Memorize in GMAT Quant for the GMAT [#permalink]  12 Jul 2013, 12:51
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One thing that I learned, more like stumbled upon, while preparing was that if you are to square any number, the just multiple the number before and after that number, and then add 1.

i.e. $$(n-1)*(n+1) + 1 = n^2$$

For example:
$$5^2 = 25$$ or
$$(5-1)*(5+1) +1 = 4*6 +1 = 24 + 1 = 25$$

Try any number and it'll work. I just find it a tad bit simpler to work with big or uncommon numbers.

Hope this helps!
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Re: What to Memorize in GMAT Quant for the GMAT [#permalink]  16 Jul 2013, 11:17
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Convert Recurring Decimal into Fraction

I saw this on the Toolkit's questions and thought it would be good that everyone knows this.

To convert a recurring decimal to fraction: (Example to be used: 0.84027840278402784027)
1. Separate the recurring number from the decimal fraction (i.e. from the number above this step will produce 84027) - This number is now going to be the numerator
2. Count the number of digits in the number (In this case it will be 5)
3. In the denominator write down 9 the same number of times as the number found in step 3 (i.e. 9 to be write five times making the denominator 99999)

Thus the fraction is now the numerator from step 1 and the denominator from step 3 (i.e. 0.840278402784027840278402784027 = 84027/99999)

Try this with any recurring number. I am not too sure but I think the properties being used here are the ones of numbers 9 and 11. Please confirm if this assumption is correct.
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Re: What to Memorize in GMAT Quant for the GMAT [#permalink]  22 Jul 2013, 20:41
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RnH wrote:
One thing that I learned, more like stumbled upon, while preparing was that if you are to square any number, the just multiple the number before and after that number, and then add 1.

i.e. $$(n-1)*(n+1) + 1 = n^2$$

Also, think about why it is so.

$$(n-1)*(n+1) = (n^2 - n + n - 1) = n^2 - 1$$

Therefore, $$(n-1)*(n+1) + 1 = n^2 - 1 + 1 = n^2$$
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Re: What to Memorize in GMAT Quant for the GMAT [#permalink]  22 Jul 2013, 21:21
VeritasPrepKarishma wrote:
RnH wrote:
One thing that I learned, more like stumbled upon, while preparing was that if you are to square any number, the just multiple the number before and after that number, and then add 1.

i.e. $$(n-1)*(n+1) + 1 = n^2$$

Also, think about why it is so.

$$(n-1)*(n+1) = (n^2 - n + n - 1) = n^2 - 1$$

Therefore, $$(n-1)*(n+1) + 1 = n^2 - 1 + 1 = n^2$$

Exactly! I had problems with higher multiples of 7 and this helped me get over the issue.
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Re: What to Memorize in GMAT Quant for the GMAT [#permalink]  16 Oct 2013, 00:34
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bb wrote:

What to Memorize in GMAT Quant for the GMAT

There are a few things you can memorize for GMAT Quant that will help you answer questions faster, minimize mistakes, and fill in any gaps and holes.
This post collects the best tips from GMAT Club with special credit going to einstein10.

Attachment:
Arithmetic Fractions and Percentages.pdf
Attachment:
what_to_remember_gmat_Q.pdf

Also some fun rules for not memorizing:

Multiples of 11
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.
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

For Multiples of 25
Multiplying 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
3) Combine:
4225

Have your own? Share them here!

we ll here learn how to find sq root of large nos.

first we must know that square of any no. does not end with i.e(last digit of the squared no.) 2,3,7 & 8.

If Last digit of the square (LHS) then last digit of the of sq. root(RHS) or vice versa
1....................................1 or 9
4....................................2 or 8
9....................................3 or 7
6....................................4 or 6
5.................................... 5
0.....................................0

for eg. the sq root of a no. ending in 1 could be 9 or 1. sq.rt of 81 = 9 , and sq. rt of 1 = 1.

nows lets see how to find sq rt of 5184

so in the above example our last digit is 4(LHS) hence the last digit of our ans could be 2 or 8. (RHS).
secondly we know 5184 is between 4900 and 6400. so the sq. rt of both these nos. 70 and 80 respectively. so our ans lies between 70 and 80
that means it could be 72 or 78.
but as we look at our no. 5184 . It is more closer to 4900 than it is to 6400.
therefore our ans has to be 72.
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Re: What to Memorize in GMAT Quant for the GMAT [#permalink]  11 Apr 2015, 22:26
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Re: What to Memorize in GMAT Quant for the GMAT [#permalink]  16 Apr 2015, 18:55
Can anyone explain the significance of the grouping of numbers on the first page of the "what to remember" PDF file? it goes from 14-240? Is the file incomplete or am I missing something? Was something cut off? Thanks
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Re: What to Memorize in GMAT Quant for the GMAT [#permalink]  14 Oct 2015, 22:52
FTS185 wrote:
Can anyone explain the significance of the grouping of numbers on the first page of the "what to remember" PDF file? it goes from 14-240? Is the file incomplete or am I missing something? Was something cut off? Thanks

Hi,
Those are the tables of the numbers that head the column i.e 14, 16, 17,... 24.

Hope this helps!!!
Re: What to Memorize in GMAT Quant for the GMAT   [#permalink] 14 Oct 2015, 22:52
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