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Probability that number is neither even nor multiple of 3

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Probability that number is neither even nor multiple of 3

by Vemuri » Sun Mar 22, 2009 2:32 am
The integers from 1 to 100 inclusive are each written on a single slip of paper and dropped into a jar. If one slip of paper is removed at random, approximately what is the probability that the number on it is neither even nor a multiple of 3?

A. 83%
B. 67%
C. 50%
D. 33%
E. 17%
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IMO D

by Dream Weaver » Sun Mar 22, 2009 2:46 am
IMO D (33%)

My approach could be wrong, so please specify the OA. But, here's how I conclude :

Probability of finding an even number is 50/100
Probability of finding a multiple of 3 is 33/100
Probability of finding an even number which is also a multiple of 3 is 16/100

So, I arrive to the probability of finding a even number or a multiple of 3 to be 50/100 + 33/100 - 16/100 = 67/100

What we need is opposite of this : 1- 67/100 = 33/100

Please specify the OA. Thanks !!
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Re: IMO D

by Vemuri » Sun Mar 22, 2009 3:06 am
Hi Dream Weaver,

Your approach & answer are both correct :wink:
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Thanks Vemuri

by Dream Weaver » Sun Mar 22, 2009 3:10 am
:D
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Re: IMO D

by KICKGMATASS123 » Mon Mar 23, 2009 12:40 pm
How do u find an even number that is also a multiple of 3 number?

Is there an approach to this?

Thanks in advance
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by RBurroughs » Mon Mar 23, 2009 9:57 pm
I did this pretty quick in my head.

1/3 are multiples of 3, and 1/2 are even[ (3) odd, (6) even, 9 (odd)...]

so keeping true 1/2 are odd/even, 1/2 of the 66 left are odd, or 33%
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Re: IMO D

by RBurroughs » Mon Mar 23, 2009 9:58 pm
KICKGMATASS123 wrote:How do u find an even number that is also a multiple of 3 number?

Is there an approach to this?

Thanks in advance
1/3 are multiples of 3, 1/2 of these are even.

1/3*1/2 = 1/6
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