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# Typical GMAT questions for Counting problems

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Manager
Joined: 29 Aug 2007
Posts: 110
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Typical GMAT questions for Counting problems [#permalink]  14 Sep 2007, 06:45
Guys ,

Can you please help me out and check my work below? I am trying to make sure I got these counting problems under control

Eg 1 . How many integers are between 51 and 107

( 107 - 51 ) + 1= 57

Eg 2 . How many integers are divisible by 3 between 100 - 200

First Integer divisible = 102
Last integer divisble = 198

3( 51 , 52 .... 66)

Number of integers ( 66 - 51) + 1 = 33

Eg 3 . What is the sum of integers between (100 and 200)

Total = Average * number of integers

Average = 100 + 200 / 2 = 150

Number of integers = ( 200 - 100) 100 + 1 = 101

Total = 101 * 150

any more counting problems , I should be aware of ?

Thanks a lot guys!!
Senior Manager
Joined: 28 Jun 2007
Posts: 320
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Re: Typical GMAT questions for Counting problems [#permalink]  14 Sep 2007, 07:49
beatgmat wrote:
Eg 2 . How many integers are divisible by 3 between 100 - 200

First Integer divisible = 102
Last integer divisble = 198

3( 51 , 52 .... 66)

Number of integers ( 66 - 51) + 1 =
33

The part in red is wrong but somehow you got the final answer right. 3 multiplied by 51 does not give 102. Also, 66 - 51 + 1 is not 33.

The correct calculation:

3(34, 35 .... 66)

Number of integers ( 66 - 34) + 1 = 33
Re: Typical GMAT questions for Counting problems   [#permalink] 14 Sep 2007, 07:49
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