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?
Answer: Option
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:
107 comments Page 2 of 11.
Tushar said:
7 years ago
Among the 20 numbers multiples of 3=20/3 which is 6. And similarly, multiples of 5 are=20/5 which are 4. Now total multiples are 10. Now among these 10 multiples, we have one common multiple that is 15.
Now remaining multiples=total multiples -common multiple.
=10-1.
=9.
Now required prob =9/20.
Now remaining multiples=total multiples -common multiple.
=10-1.
=9.
Now required prob =9/20.
Souravbaidya said:
1 decade ago
A circular dartboard of radius 1 foot is at a distance of 20 feet from you. You throw a dart at it and it
hits the dartboard at some point Q in the circle. What is the probability that Q is closer to the center
of the circle than the periphery?
a) 0.75 b) 1 c) 0.5 d) 0.25
hits the dartboard at some point Q in the circle. What is the probability that Q is closer to the center
of the circle than the periphery?
a) 0.75 b) 1 c) 0.5 d) 0.25
Ravi said:
9 years ago
According to me, From 1 to 20, numbers its 1, 2, 3, 4....., 19, 20 then number which is a multiple of 3 or 5.
Lets take 3 (3, 6, 9, 12, 15, 18 and 5 = (5, 10, 15, 20).
So in 3 we have 6 and 5 we have 4 so it's 6/20 and 4/20 and 1/20.
Solution = 6 + 4 - 1/20 == 9/20 answer.
Lets take 3 (3, 6, 9, 12, 15, 18 and 5 = (5, 10, 15, 20).
So in 3 we have 6 and 5 we have 4 so it's 6/20 and 4/20 and 1/20.
Solution = 6 + 4 - 1/20 == 9/20 answer.
Ravi said:
9 years ago
According to me, From 1 to 20, numbers its 1, 2, 3, 4....., 19, 20 then number which is a multiple of 3 or 5.
Lets take 3 (3, 6, 9, 12, 15, 18 and 5 = (5, 10, 15, 20).
So in 3 we have 6 and 5 we have 4 so it's 6/20 and 4/20 and 1/20.
Solution = 6 + 4 - 1/20 == 9/20 answer.
Lets take 3 (3, 6, 9, 12, 15, 18 and 5 = (5, 10, 15, 20).
So in 3 we have 6 and 5 we have 4 so it's 6/20 and 4/20 and 1/20.
Solution = 6 + 4 - 1/20 == 9/20 answer.
Pawan said:
1 decade ago
Hi Guys ..
according to me the answer is 2/5
A = multiple of 3
B = multiple of 5
P(A U B) = P(A) + P(B) - P(A n B)
n(A) = 6 ( 3,6,9,12,15,18)
n(B) = 3 (5,10,15)
n (A n B) = 1 (15 --> this comes in both)
Hence, prob = 6/20 + 3/20 - 1/20 = 8/20 = 2/5
according to me the answer is 2/5
A = multiple of 3
B = multiple of 5
P(A U B) = P(A) + P(B) - P(A n B)
n(A) = 6 ( 3,6,9,12,15,18)
n(B) = 3 (5,10,15)
n (A n B) = 1 (15 --> this comes in both)
Hence, prob = 6/20 + 3/20 - 1/20 = 8/20 = 2/5
V S Abhirame said:
7 years ago
@Souravbaidya.
Circular board of i feet has area Pi. The area of the region containing all points which are closed to center than to periphery will be Pi/4. Hence the proportion to hit near the center is 1/4=.25. So, D is the correct answer.
Circular board of i feet has area Pi. The area of the region containing all points which are closed to center than to periphery will be Pi/4. Hence the proportion to hit near the center is 1/4=.25. So, D is the correct answer.
Sriram said:
3 years 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.
The total number is 10.
So,
10/20 = 1/2.
(39)
Nikhil Merwade said:
1 decade ago
Why can't we use the formula of nCr...??...
1 ticket can be selected from 20 tickets in 20C1 ways.
Ticket removed is a multiple of 3 or 5 will be 20C6 * 20C4
Answer will be (20C6 * 20C4)/20C1...
Why can't this be proper method?
1 ticket can be selected from 20 tickets in 20C1 ways.
Ticket removed is a multiple of 3 or 5 will be 20C6 * 20C4
Answer will be (20C6 * 20C4)/20C1...
Why can't this be proper method?
Rach said:
1 decade ago
Circular board of i feet has area Pi. The area of the region containing all points which are closed to center than to periphery will be Pi/4. Hence the proportion to hit near the center is 1/4=.25. So D is the correct answer.
Prawesh Pradhan said:
9 years ago
From 1 to 20, numbers which are divisible by 3 are 3, 6, 9, 12, 15 & 18 -> total 6.
Numbers divisible by 5 are 5, 10, 15, 20 total 4.
So, 6 + 4 = 10. But 15 is counted twice. Therefore 10 - 1= 9. Result is 9/20.
Numbers divisible by 5 are 5, 10, 15, 20 total 4.
So, 6 + 4 = 10. But 15 is counted twice. Therefore 10 - 1= 9. Result is 9/20.
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