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# In a set of numbers from 100 to 1000 inclusive, how many

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Manager
Joined: 02 Aug 2007
Posts: 145

Kudos [?]: 51 [0], given: 0

In a set of numbers from 100 to 1000 inclusive, how many [#permalink]

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14 Nov 2007, 17:51
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In a set of numbers from 100 to 1000 inclusive, how many integers are odd and do not contain the digit "5"?

a. 180
b. 196
c. 286
d. 288
e. 324

Kudos [?]: 51 [0], given: 0

Manager
Joined: 08 Nov 2007
Posts: 97

Kudos [?]: 3 [0], given: 0

Re: PS - Odd Numbers without 5 [#permalink]

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14 Nov 2007, 17:52
yuefei wrote:
In a set of numbers from 100 to 1000 inclusive, how many integers are odd and do not contain the digit "5"?

a. 180
b. 196
c. 286
d. 288
e. 324

Can someone please explain the best approach to these types of questions, other than sitting down and counting them one by one?

Kudos [?]: 3 [0], given: 0

Manager
Joined: 02 Aug 2007
Posts: 145

Kudos [?]: 51 [0], given: 0

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14 Nov 2007, 18:00
Using the probability method:

N = 1000 - 100 = 900
P = (8/9)*(9/10)*(4/10) = 288/900

N*P = 900*(288/900) = 288

However, this is not the OA. Anyone?

Kudos [?]: 51 [0], given: 0

Director
Joined: 09 Aug 2006
Posts: 754

Kudos [?]: 267 [0], given: 0

Re: PS - Odd Numbers without 5 [#permalink]

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14 Nov 2007, 20:57
yuefei wrote:
In a set of numbers from 100 to 1000 inclusive, how many integers are odd and do not contain the digit "5"?

a. 180
b. 196
c. 286
d. 288
e. 324

Getting 288. What's the source of the question?

Kudos [?]: 267 [0], given: 0

Manager
Affiliations: CFA L3 Candidate, Grad w/ Highest Honors
Joined: 03 Nov 2007
Posts: 131

Kudos [?]: 147 [0], given: 9

Location: USA
Schools: Chicago Booth R2 (WL), Wharton R2 w/ int, Kellogg R2 w/ int
WE 1: Global Operations (Futures & Portfolio Financing) - Hedge Fund (\$10bn+ Multi-Strat)
WE 2: Investment Analyst (Credit strategies) - Fund of Hedge Fund (\$10bn+ Multi-Strat)

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14 Nov 2007, 21:21
M03-12 of the GMAT exams. 288 IS the right answer

yuefei, Dont confuse me anymore then I already am!

~

Kudos [?]: 147 [0], given: 9

Director
Joined: 11 Jun 2007
Posts: 909

Kudos [?]: 296 [0], given: 0

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14 Nov 2007, 23:05
what the... i also get 288. perhaps the OA is not right

Kudos [?]: 296 [0], given: 0

CEO
Joined: 21 Jan 2007
Posts: 2734

Kudos [?]: 1091 [0], given: 4

Location: New York City

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23 Nov 2007, 14:20
The OA is D. This is a Challenges question.

Kudos [?]: 1091 [0], given: 4

CEO
Joined: 21 Jan 2007
Posts: 2734

Kudos [?]: 1091 [0], given: 4

Location: New York City

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24 Nov 2007, 00:51
pmenon wrote:
can someone explain why it is 8, 9 and 4 ?

the range is from 100 to 1000. 1000 is even.therefore we work with only 3 digit numbers.

focusing only on the hundreds digit place, there are 8 possibilities for that place. we cannot have 5 or 0 because a number cannot start with 0.

focusing only on the tens digit place, we can have any number except 5. Therefore, 9 possibilities.

focusing only on the units digit place, we can only have odd digits. There are 5 odd digits. We cannot have one of the odd digits, the number 5. Therefore 4 possible numbers

8*9*4 =288

Kudos [?]: 1091 [0], given: 4

24 Nov 2007, 00:51
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