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m22 #8

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Director
Joined: 03 Sep 2006
Posts: 862

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m22 #8 [#permalink]

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09 May 2010, 13:05
What is the probability that one of the two integers randomly selected from range 20-29 is prime and the other is a multiple of 3?

(The numbers are selected independently of each other, i.e. they can be equal)

Kudos [?]: 1125 [0], given: 33

Manager
Joined: 20 Apr 2010
Posts: 151

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Location: I N D I A
Re: m22 #8 [#permalink]

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11 May 2010, 22:21
Prime number in the range 20 - 29 is 23 only.
Multiples of 3 in this range are - 21 , 24 , 27

Probability = 1/10 ( Probability of getting 1 Prime no. out of total 10 numbers ) * 3/9 ( Probability of getting multiple of 3 out of remaining 9)

= 3/90 = 1/30.

Hope its correct..

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Current Student
Joined: 31 Mar 2010
Posts: 167

Kudos [?]: 32 [0], given: 4

Schools: Tuck Class of 2013
Re: m22 #8 [#permalink]

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13 May 2010, 08:22
LM wrote:
What is the probability that one of the two integers randomly selected from range 20-29 is prime and the other is a multiple of 3?

(The numbers are selected independently of each other, i.e. they can be equal)

There are two primes within the 20-29 range = 23 and 29. So P=2/10
There are three numbers that are multiple of 3: 21, 24 and 27. So P=3/10

So to have one AND the other (2/10)*(3/10) = 3/50

What is the OA ?

Thanks,

Kudos [?]: 32 [0], given: 4

Re: m22 #8   [#permalink] 13 May 2010, 08:22
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m22 #8

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