Aptitude - Probability - Discussion

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Tickets numbered 1 to 20 are mixed up and then a ticket is drawn at random. What is the probability that the ticket drawn has a number which is a multiple of 3 or 5?

[A].

[B].

[C].

[D].

Answer: Option D

Explanation:

Here, S = {1, 2, 3, 4, ...., 19, 20}.

Let E = event of getting a multiple of 3 or 5 = {3, 6 , 9, 12, 15, 18, 5, 10, 20}.

P(E) = n(E) = 9 .

n(S) 20

Sundar said: (Fri, Jun 18, 2010 10:32:27 AM)

Here, S = {1, 2, 3, 4, ...., 19, 20}. Let E = event of getting a multiple of 3 or 5 = {3, 6 , 9, 12, 15, 18, 5, 10, 15, 20}. P(E) = 1/2. Is this correct? Please give your thoughts on this.

Manju said: (Wed, Jul 21, 2010 07:07:32 PM)

yes 1/2 is the right ans..coz 15 is a multiple of 5 and its not included.

Karthik said: (Thu, Jul 22, 2010 12:48:19 PM)

No. You are wrong Sundar. Because, 15 has already consider once so there is no need to consider it again. So the answer is 9/20.

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