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## Difficult Math Question #33 - Probability

This topic has 4 member replies
800guy Master | Next Rank: 500 Posts
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#### Difficult Math Question #33 - Probability

Mon Oct 23, 2006 2:27 pm
A number is selected at random from first 30 natural numbers. What is the probability that the number is a multiple of either 3 or 13?

(A) 17/30
(B) 2/5
(C) 7/15
(D) 4/15
(E) 11/30

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800guy Master | Next Rank: 500 Posts
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Wed Oct 25, 2006 3:29 pm
here's the OA:
Total no from 1 to 30 = 30
total no from 1 to 30 which r multiple of 3 = 10 (eg(3,6,9,12,15,18,21,24,27,30))
total no from 1 to 30 which r multiple of 13 = 2 (eg 13,26)
P(a or b ) = p(a) + p(b)
p(a)= 10/30
p(b)=2/30
p(a) + p(b) = 10/30+2/30 = 2/5

limits660 Senior | Next Rank: 100 Posts
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Wed Oct 25, 2006 4:23 am
I believe its B

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Jeff Sacco
www.jeffsacco.ca

800guy Master | Next Rank: 500 Posts
Joined
27 Jun 2006
Posted:
354 messages
Followed by:
5 members
11
Wed Oct 25, 2006 3:29 pm
here's the OA:
Total no from 1 to 30 = 30
total no from 1 to 30 which r multiple of 3 = 10 (eg(3,6,9,12,15,18,21,24,27,30))
total no from 1 to 30 which r multiple of 13 = 2 (eg 13,26)
P(a or b ) = p(a) + p(b)
p(a)= 10/30
p(b)=2/30
p(a) + p(b) = 10/30+2/30 = 2/5

limits660 Senior | Next Rank: 100 Posts
Joined
12 Jul 2006
Posted:
57 messages
Followed by:
2 members
Wed Oct 25, 2006 4:23 am
I believe its B

_________________
-
Jeff Sacco
www.jeffsacco.ca

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