# Aptitude - Probability - Discussion

Discussion Forum : Probability - General Questions (Q.No. 1)
1.
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?
 1 2
 2 5
 8 15
 9 20
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

Discussion:
103 comments Page 1 of 11.

Ephrem Alemu Mantose ETH said:   2 months ago
P(A U B) = P(A) + P(B) - P(AnB),
= 6/20 + 4/20 - 1/20,
= 9/20.

Tanya said:   2 months ago
Yes, 9/20 is the correct option because 15 is a multiple of both 3 and 5.
So we considered it only once (either with 3 or either with 5).
(5)

PURVA said:   8 months ago
@All.

Here is my solution.
P(A or B) = P(A) + P(B) -P(A AND B).
P(3) = 6/20 {3,6,9,12,15,18},
P(5) = 4/20 {5,10,15,20},
P(3 and 5) = 1/20 {15}.
(11)

Sriram said:   9 months ago
The multiple of 3 and 5 is given numbers 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,7,18,19,20. While the question is about the multiple of 3 is 3,6,9,12,15,18 and the multiple of 5 is 5,10,15,20.
The total number is 10.
So,
10/20 = 1/2.
(25)

Abhishek tomar said:   1 year ago
15 is the multiple of 3 and 5. while question is about the multiple of 3 or 5 so, why not option C?
(6)

Niraml said:   1 year ago
Here, the total ticket is 20 we gonna take 1 from that 20 tickets it can be multiple of 3 or 5
so,

5C1 + 3C1/20C1 = 5+3/20 = 8/20.

= 2/5 is correct.

Avaneet Agrahari said:   3 years ago
Multiple of 3=[,3,6,912,15,18]=6
M....o. 5=[5,10,15,20]=4 but 15 is already in 3 so it count 3
Ans= 6+3/20=9/20
(8)

Kavya said:   4 years ago
@Uday,

15 is repeated.
And 5 is missing.
(3)

Kousalya said:   4 years ago
Yes, I too agree 1/2 is the right answer.

Uday said:   4 years ago
(3, 6,9,12,15,18,5,10,15,20).
= 10/20,
= 1/2.
(1)